Remove Goma builds and support in gn_flavor.

The experiment with using Goma to speed up Windows compiles was very
close to being successful, but at this point the ongoing maintenance
does not seem to be worth the 50-70 seconds saved.

Change-Id: Ie3900b9a681e448a3e47634efbab7695ebccad33
Reviewed-on: https://skia-review.googlesource.com/114363
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
9 files changed