Fix git-llvm crashing when trying to remove directory while cleaning
Fix git-llvm crashing when trying to remove directory while cleaning

Summary:
I'm trying to push D59198 but it seems that `git-llvm push` can't handle the fact
that I add a new directory in the patch:

```
> git llvm push -n
Pushing 1 commit:
  e7c0a9bd136 Correctly look up declarations in inline namespaces
Traceback (most recent call last):
  File "llvm/utils/git-svn//git-llvm", line 431, in <module>
    args.func(args)
  File "llvm/utils/git-svn//git-llvm", line 385, in cmd_push
    clean_svn(svn_root)
  File "llvm/utils/git-svn//git-llvm", line 201, in clean_svn
    os.remove(os.path.join(svn_repo, filename))
IsADirectoryError: [Errno 21] Is a directory: '.git/llvm-upstream-svn/lldb/trunk/packages/Python/lldbsuite/test/expression_command/inline-namespace'
```

This patch just uses shutil to delete the directory instead of trying to use `os.remove`
which only works for files.

Reviewers: mehdi_amini, jlebar

Reviewed By: jlebar

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59236

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@355896 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm