Remove runIndex as a concept for GrTextBlob

Change-Id: I8ac756a088c1dddf475bf96f9a4a84ec2cb500be
Reviewed-on: https://skia-review.googlesource.com/c/169763
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
5 files changed