Revert "Mark GLSL reserved names as reserved in SkSL grammar."

This reverts commit 57f3fc4cde764c098666acdac05a7c905508fb2d.

Reason for revert: breaking Android roll

Original change's description:
> Mark GLSL reserved names as reserved in SkSL grammar.
>
> We now reject every reserved name in the ES2 docs as an unexpected
> token, except for the rule that all names beginning with `gl_` are
> reserved. (Unfortunately, sksl_frag bends the rules by directly
> declaring a builtin variable named `gl_SecondaryFragColorEXT`.)
>
> Change-Id: I5dcb40b754720ca97fe3d80e2f9072beaa39fcdb
> Bug: skia:11115
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/454737
> Auto-Submit: John Stiles <johnstiles@google.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

Bug: skia:11115
Change-Id: Ica56f48dc76ef1e52780acaf59b8ad9143637637
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/454860
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
83 files changed