Revert "Implement tracking of BUILD.gn files ..."

This change reverts reverts commit 44fd682d (#483337);
it looks like it doesn't correctly handle at least
changes to the default configs.

[email protected], [email protected], [email protected]
BUG=755622

Change-Id: Ic8ad61736ad208bcce6004e8047febf405c001e1
Reviewed-on: https://chromium-review.googlesource.com/617774
Commit-Queue: Dirk Pranke <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#495174}
48 files changed