[glcient] Delete unused import

Change-Id: I6f2b22a561e823455f5e1af26a88ed7d8c0a896d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6444535
Commit-Queue: Allen Li <ayatane@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>

gclient_scm.py

@@ -24,7 +24,6 @@ import gerrit_util
 import git_auth
 import git_cache
 import git_common
-import newauth
 import scm
 import subprocess2