Reland "remove the OpMemoryPool"

Add ClearCache() {} to the non-caching case.

This is a reland of cfdae5a56cc005f56afd444c655d1ad5108de598

Original change's description:
> remove the OpMemoryPool
>
> Change-Id: I987384f8009445ba8308e85b75daf4880a8d36be
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/383957
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Herb Derby <herb@google.com>

Change-Id: I03f80ba61f5643c40f812a9687b12a5d2aa663b1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/385276
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
diff --git a/src/gpu/ops/GrAtlasTextOp.cpp b/src/gpu/ops/GrAtlasTextOp.cpp
index 3b037ba..b2b9b25 100644
--- a/src/gpu/ops/GrAtlasTextOp.cpp
+++ b/src/gpu/ops/GrAtlasTextOp.cpp
@@ -35,7 +35,7 @@
 #include <utility>
 
 // If we have thread local, then cache memory for a single GrAtlasTextOp.
-#if !defined(GR_OP_ALLOCATE_USE_POOL) && defined(GR_HAS_THREAD_LOCAL)
+#if defined(GR_HAS_THREAD_LOCAL)
 static thread_local void* gCache = nullptr;
 void* GrAtlasTextOp::operator new(size_t s) {
     if (gCache != nullptr) {