Revert "Rewrite switch statements in GLSL strict-ES2 mode."

This reverts commit 45e3838006df8bc393fe6f4ca1cff999b41167f4.

Reason for revert: Also need to rewrite them in actual ES2 mode.

Original change's description:
> Rewrite switch statements in GLSL strict-ES2 mode.
>
> Once this lands, switch statements will work everywhere--Metal, SPIR-V,
> GLSL, and SkVM.
>
> Change-Id: I2797d0a872de8be77bb9f7aa6acb93421d571d70
> Bug: skia:12450
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/452356
> Commit-Queue: John Stiles <johnstiles@google.com>
> Auto-Submit: John Stiles <johnstiles@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>

Bug: skia:12450
Change-Id: I92656ed40289872405c0873f2c56a52b04e35b1d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/452556
Auto-Submit: Brian Osman <brianosman@google.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
7 files changed