Remove GrBatch::renderTarget() and use GrBatch::renderTargetUniqueID() instead.

Change-Id: I621ed38955e374c79a4d44c0020f9bae9655f001
Reviewed-on: https://skia-review.googlesource.com/5344
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
8 files changed