Remove GrBuffer::mapPtr()

Only used in an assert.

Change-Id: Iecfd853a71d7dd1c22096886465843c7a0122c74
Reviewed-on: https://skia-review.googlesource.com/c/187380
Auto-Submit: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
2 files changed