GitLab

This manifest key was never completely implemented and there are no
plans to do so as well. Remove the key and associated code.

TODO: Also remove this key from
https://developer.chrome.com/docs/extensions/mv2/manifest/.

BUG=135628, 1164954

Change-Id: Ia6b11e04f68ca80ea4c91fe1d7a67266f14743b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2621972Reviewed-by: David Bertoni <dbertoni@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842162}