build: setup: only try removing the working dir from the path if its on it
build: setup: only try removing the working dir from the path if its on it

The existance of a thrown exception in setup.py on my box was causing
a test failure for me:

ERROR: test_retry_kwargs_can_be_empty (celery.tests.tasks.test_tasks.test_task_retries)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/var/unsecure/src/celery/celery/tests/tasks/test_tasks.py", line 133, in test_retry_kwargs_can_be_empty
    retry_task_mockapply.retry(args=[4, 4], kwargs=None)
  File "/var/unsecure/src/celery/celery/app/task.py", line 563, in retry
    maybe_reraise()
  File "setup.py", line 15, in <module>
    sys.path.remove(path)
ValueError: list.remove(x): x not in list

cbrepo/celery,ask/celery,cbrepo/celery,ask/celery