Remove BUG_LINE_FORMAT from codereview.settings

The Bug: style (a Gerrit footer) is used by git-cl for Gerrit changes as
of 3a16ed155e3f.

Bug: chromium:681184
Change-Id: I58c29b6908aee57c7f03374180148f241af91b22
Reviewed-on: https://chromium-review.googlesource.com/461481
Reviewed-by: Scott Graham <scottmg@chromium.org>

codereview.settings

@@ -17,5 +17,4 @@ GERRIT_SQUASH_UPLOADS: True
 CODE_REVIEW_SERVER: https://canary-chromium-review.googlesource.com/
 VIEW_VC: https://chromium.googlesource.com/crashpad/crashpad/+/
 PROJECT: crashpad
-BUG_LINE_FORMAT: Bug: %s
 BUG_PREFIX: crashpad: