cleanup: remove redundant import
For some reason the import checker only caught this on py3.
Differential Revision: https://phab.mercurial-scm.org/D6657
--- a/tests/test-bookmarks-corner-case.t Thu Jul 18 21:10:17 2019 +0530
+++ b/tests/test-bookmarks-corner-case.t Thu Jul 18 14:19:41 2019 -0400
@@ -119,7 +119,6 @@
> import atexit
> import os
> import time
- > import atexit
> from mercurial import error, extensions, bookmarks
>
> def wait(repo):