Don't try to remove .repo if it doesn't exist

Part of the cleanup path for _Init is removing the .repo
directory. However, _Init can fail before creating the .repo directory,
so trying to remove it raises another exception:

    fatal: invalid branch name 'refs/changes/53/55053/4'
    Traceback (most recent call last):
      File "/home/mitchelh/bin/repo", line 775, in <module>
        main(sys.argv[1:])
      File "/home/mitchelh/bin/repo", line 749, in main
        os.rmdir(repodir)
    OSError: [Errno 2] No such file or directory: '.repo'

Fix this by only removing .repo if it actually exists.

Change-Id: Ia251d29e9c73e013eb296501d11c36263457e235
1 file changed