Although git-cl-upload warns when uploading a new patchset
to a change owned by someone else, if the uploader has run
'git cl issue 0', then git-cl believes they'll be uploading
a new change, so it doesn't bother checking. However, once
the upload begins, Gerrit notices the Change-Id in the commit
message, and instead adds a new patchset to someone else's
review (if the uploader is a committer).

This change introduces some logic to git-cl-issue to also
remove any Change-Id from the commit message when a user
tries to clear the metadata about their branch.

Bug: 741648
Change-Id: I6c7c3b24a7fc09c68220c8200b732fbdf9cf1fd3
Reviewed-on: https://chromium-review.googlesource.com/568267Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>