Revert "support for 'half' types in sksl, plus general numeric type improvements"

This reverts commit 93061b53442ce303e9d3ef74c7eeddc034802c4f.

Reason for revert: bot failures

Original change's description:
> support for 'half' types in sksl, plus general numeric type improvements
> 
> Bug: skia:
> Change-Id: Id285262fda8291847f11343d499b5df62ddb4b09
> Reviewed-on: https://skia-review.googlesource.com/28980
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

TBR=bsalomon@google.com,ethannicholas@google.com

Change-Id: Ie8672271d35b9fcdf567f8bc3674084748be66ad
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/29600
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
16 files changed