Revert "Add Ganesh support for RGBA_16161616 and RG_half"

This reverts commit 156622513ffc385bb493eda8d4cf5cbed19350d1.

Reason for revert: valgrind

Original change's description:
> Add Ganesh support for RGBA_16161616 and RG_half
> 
> Change-Id: Ia424ff719c5fb8d1842a909ade09ad6f5f78f21f
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/219998
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

TBR=egdaniel@google.com,robertphillips@google.com

Change-Id: I7a8e99e70f575fb301ce289d9a04ebbec25b934b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/220739
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
22 files changed