Revert "Wrap page index packing in helper methods."

This reverts commit cb93a20d9a961219bad674d6c168bfde03a16246.

Reason for revert: Still seeing some corruption issues with Chrome text that may be related to this.

Original change's description:
> Wrap page index packing in helper methods.
> 
> Also simplifies the shaders if we know there's only one atlas texture.
> 
> Change-Id: I81063d423fd56cf91caee83ba9eae9d988aa249b
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/266566
> Commit-Queue: Jim Van Verth <jvanverth@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>

TBR=jvanverth@google.com,herb@google.com,brianosman@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I031f27c07929b1f66581ed8e94e1056d9107bf75
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/266633
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
8 files changed