Revert "Replace pooling mechanism with GrMemoryPool."

This reverts commit 67e1cf4b1d81185051bdaaaab4a1d88723e57358.

Reason for revert: iOS 8

Original change's description:
> Replace pooling mechanism with GrMemoryPool.
>
> This change is a wash for tests that could fit inside the previous
> hard-coded pool (512 nodes) and appears to be a 5% improvement for
> sksl_large. Larger programs would hypothetically show an even more
> significant improvement.
>
> When SK_SUPPORT_GPU is disabled, we disable pooling entirely and fall
> back to the system allocator. This is necessary because SkSL can exist
> without Ganesh (such as in the wasm+CanvasKit build).
>
> Nanobench: http://screen/4xJEzdGducRxGeq
>
> Change-Id: I71dc702a84ab5c163673e35ec651003d7d45dacd
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/330219
> Commit-Queue: John Stiles <johnstiles@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>
> Auto-Submit: John Stiles <johnstiles@google.com>

TBR=brianosman@google.com,ethannicholas@google.com,johnstiles@google.com

Change-Id: I26dbd7f2d5348dd717c39fd0780ee5d140292e9a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/330416
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
6 files changed