More GrPipeline cleanup.

Remove CanCombine and AreEqual (unused)

Remove isInitialized() now that pipelines are initialized at creation.

Change-Id: Ibacf81d1f879c7ef9ea91a8f471c3d1df3eb2fed
Reviewed-on: https://skia-review.googlesource.com/29020
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
3 files changed