[SPARK-32303][PYTHON][TESTS] Remove leftover from editable mode installation in PIP test
[SPARK-32303][PYTHON][TESTS] Remove leftover from editable mode installation in PIP test

### What changes were proposed in this pull request?

Currently the Jenkins PIP packaging test fails as below intermediately:

```
Installing dist into virtual env
Processing ./python/dist/pyspark-3.1.0.dev0.tar.gz
Collecting py4j==0.10.9 (from pyspark==3.1.0.dev0)
  Downloading https://files.pythonhosted.org/packages/9e/b6/6a4fb90cd235dc8e265a6a2067f2a2c99f0d91787f06aca4bcf7c23f3f80/py4j-0.10.9-py2.py3-none-any.whl (198kB)
Installing collected packages: py4j, pyspark
  Found existing installation: py4j 0.10.9
    Uninstalling py4j-0.10.9:
      Successfully uninstalled py4j-0.10.9
  Found existing installation: pyspark 3.1.0.dev0
Exception:
Traceback (most recent call last):
  File "/home/anaconda/envs/py36/lib/python3.6/site-packages/pip/_internal/cli/base_command.py", line 179, in main
    status = self.run(options, args)
  File "/home/anaconda/envs/py36/lib/python3.6/site-packages/pip/_internal/commands/install.py", line 393, in run
    use_user_site=options.use_user_site,
  File "/home/anaconda/envs/py36/lib/python3.6/site-packages/pip/_internal/req/__init__.py", line 50, in install_given_reqs
    auto_confirm=True
  File "/home/anaconda/envs/py36/lib/python3.6/site-packages/pip/_internal/req/req_install.py", line 816, in uninstall
    uninstalled_pathset = UninstallPathSet.from_dist(dist)
  File "/home/anaconda/envs/py36/lib/python3.6/site-packages/pip/_internal/req/req_uninstall.py", line 505, in from_dist
    '(at %s)' % (link_pointer, dist.project_name, dist.location)
AssertionError: Egg-link /home/jenkins/workspace/SparkPullRequestBuilder3/python does not match installed
```

- https://github.com/apache/spark/pull/29099#issuecomment-658073453 (amp-jenkins-worker-04)
- https://github.com/apache/spark/pull/29090#issuecomment-657819973 (amp-jenkins-worker-03)

Seems like the previous installation of editable mode affects other PRs.

This PR simply works around by removing the symbolic link from the previous editable installation. This is a common workaround up to my knowledge.

### Why are the changes needed?

To recover the Jenkins build.

### Does this PR introduce _any_ user-facing change?

No, dev-only.

### How was this patch tested?

Jenkins build will test it out.

Closes #29102 from HyukjinKwon/SPARK-32303.

Lead-authored-by: HyukjinKwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>
Co-authored-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>
Signed-off-by: Dongjoon Hyun <6ff48b33cbb828151035af58a92f18a39f1d1036@apache.org>

wangmiao1981/spark,wangyum/spark,taroplus/spark,shaneknapp/spark,xuanyuanking/spark,WeichenXu123/spark,holdenk/spark,zzcclp/spark,HyukjinKwon/spark,wangyum/spark,maropu/spark,cloud-fan/spark,wangmiao1981/spark,taroplus/spark,shaneknapp/spark,maropu/spark,nchammas/spark,hvanhovell/spark,jiangxb1987/spark,dbtsai/spark,WeichenXu123/spark,milliman/spark,WeichenXu123/spark,witgo/spark,dongjoon-hyun/spark,vinodkc/spark,apache/spark,gengliangwang/spark,ueshin/apache-spark,JoshRosen/spark,dongjoon-hyun/spark,vinodkc/spark,BryanCutler/spark,holdenk/spark,dbtsai/spark,shaneknapp/spark,shuangshuangwang/spark,vinodkc/spark,hvanhovell/spark,xuanyuanking/spark,wzhfy/spark,witgo/spark,wzhfy/spark,BryanCutler/spark,dongjoon-hyun/spark,jiangxb1987/spark,nchammas/spark,chuckchen/spark,hvanhovell/spark,milliman/spark,rednaxelafx/apache-spark,zero323/spark,wzhfy/spark,witgo/spark,xuanyuanking/spark,shuangshuangwang/spark,srowen/spark,maropu/spark,hvanhovell/spark,holdenk/spark,milliman/spark,wzhfy/spark,taroplus/spark,wangyum/spark,zzcclp/spark,cloud-fan/spark,chuckchen/spark,ptkool/spark,JoshRosen/spark,mahak/spark,JoshRosen/spark,chuckchen/spark,ptkool/spark,milliman/spark,ueshin/apache-spark,dongjoon-hyun/spark,srowen/spark,wangyum/spark,rednaxelafx/apache-spark,dbtsai/spark,cloud-fan/spark,srowen/spark,cloud-fan/spark,shuangshuangwang/spark,shaneknapp/spark,apache/spark,nchammas/spark,holdenk/spark,apache/spark,zzcclp/spark,nchammas/spark,xuanyuanking/spark,hvanhovell/spark,rednaxelafx/apache-spark,HyukjinKwon/spark,wangmiao1981/spark,cloud-fan/spark,jiangxb1987/spark,hvanhovell/spark,hvanhovell/spark,zero323/spark,mahak/spark,nchammas/spark,chuckchen/spark,WeichenXu123/spark,rednaxelafx/apache-spark,mahak/spark,milliman/spark,BryanCutler/spark,zzcclp/spark,mahak/spark,wzhfy/spark,nchammas/spark,jiangxb1987/spark,milliman/spark,witgo/spark,taroplus/spark,cloud-fan/spark,ueshin/apache-spark,dongjoon-hyun/spark,WeichenXu123/spark,HyukjinKwon/spark,dbtsai/spark,dbtsai/spark,taroplus/spark,vinodkc/spark,apache/spark,zero323/spark,BryanCutler/spark,wzhfy/spark,HyukjinKwon/spark,holdenk/spark,wangyum/spark,ptkool/spark,gengliangwang/spark,WeichenXu123/spark,HyukjinKwon/spark,zzcclp/spark,witgo/spark,srowen/spark,taroplus/spark,gengliangwang/spark,BryanCutler/spark,shaneknapp/spark,HyukjinKwon/spark,chuckchen/spark,chuckchen/spark,BryanCutler/spark,maropu/spark,shuangshuangwang/spark,jiangxb1987/spark,holdenk/spark,shuangshuangwang/spark,wangmiao1981/spark,JoshRosen/spark,JoshRosen/spark,dongjoon-hyun/spark,ptkool/spark,zzcclp/spark,ptkool/spark,srowen/spark,wangmiao1981/spark,wangyum/spark,ptkool/spark,vinodkc/spark,shuangshuangwang/spark,wangyum/spark,gengliangwang/spark,maropu/spark,dbtsai/spark,witgo/spark,rednaxelafx/apache-spark,maropu/spark,ueshin/apache-spark,xuanyuanking/spark,zero323/spark,xuanyuanking/spark,taroplus/spark,jiangxb1987/spark,shaneknapp/spark,maropu/spark,dbtsai/spark,ueshin/apache-spark,milliman/spark,apache/spark,ueshin/apache-spark,gengliangwang/spark,shuangshuangwang/spark,srowen/spark,nchammas/spark,zero323/spark,mahak/spark,dongjoon-hyun/spark,gengliangwang/spark,zero323/spark,ptkool/spark,holdenk/spark,mahak/spark,witgo/spark,wangmiao1981/spark,apache/spark,JoshRosen/spark,jiangxb1987/spark,wzhfy/spark,BryanCutler/spark,shaneknapp/spark,zzcclp/spark,rednaxelafx/apache-spark,rednaxelafx/apache-spark,xuanyuanking/spark,zero323/spark,WeichenXu123/spark,JoshRosen/spark,gengliangwang/spark,cloud-fan/spark,vinodkc/spark,mahak/spark,apache/spark,wangmiao1981/spark,chuckchen/spark,ueshin/apache-spark,srowen/spark,HyukjinKwon/spark,vinodkc/spark