Non-substantive GPU text changes

This CL pulls some cleanup changes out of the omnibus GPU text CL. It:

Removes the unused GrTextStrike::removeID method
Removes the unused GrTextStrike::countGlyphs method
Removes the GrTextureStrike::fAtlasedGlyphs member variable
Adds an "int SkSpan::count() const" helper method

Change-Id: I88eefd929a5576093de58af85582567d8df5610a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/280706
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Herb Derby <herb@google.com>
6 files changed