Remove all old gpu gradient code

At this point, all gradient configurations should be handled by the new
FP gradient code path so this removes all of the dead code.

Bug: skia:
Change-Id: If6041edcd8417d8f345e17000ccb27d9efea0bb3
Reviewed-on: https://skia-review.googlesource.com/152383
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
13 files changed