This reverts commit 94171749.

Reason for revert: crashes on Debug bots

Original change's description:
> Vulkan:Adding custom pool allocator
> 
> Migrated pool allocator used by compiler to common.
> 
> Planning to use this for ANGLE custom command buffers so this some
> refactoring in preparation for that work.
> 
> Added a unit test to check PoolAllocator functionality.
> 
> Bug: angleproject:2951
> Change-Id: I29618cfdb065b8a5fefd40719a35d27b1f6e99ef
> Reviewed-on: https://chromium-review.googlesource.com/c/1476953
> Reviewed-by: Jamie Madill <jmadill@google.com>
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> Commit-Queue: Tobin Ehlis <tobine@google.com>

TBR=ynovikov@chromium.org,jmadill@google.com,tobine@google.com,syoussefi@chromium.org

Change-Id: Id8c522bd1d94154e871211d975e801a55cc9c257
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:2951, angleproject:3169
Reviewed-on: https://chromium-review.googlesource.com/c/1487977Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>