[graphite] Remove PipelineDataCache index indirection

The PipelineDataCache now returns the persisted data as a stable
pointer. This simplifies the unique tracking within DrawPass::Make,
which had already been updated to use the ssbo index for sorting.

Change-Id: I9ab3c0a16c01bd8df6040ee013a89715e5b304d5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/573877
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
9 files changed