Clean up more references to GYP.

Delete files only used by GYP, and files that used GYP.  Neither can
possibly be actively used.  Beyond that, just a couple doc tweaks.

Change-Id: I0220d7226e7bb9ed7c54a7d8f2906a718313c521
Reviewed-on: https://skia-review.googlesource.com/8062
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Hal Canary <halcanary@google.com>
20 files changed