This reverts commit 05459e06.

Reason for revert: Clusterfuzz bugs flagged this commit

Original change's description:
> Vulkan: Adding custom pool allocator
> 
> Copied pool allocator used by compiler to common and hooking it up as
> custom allocator for CommandPools. Modified it to support reallocation.
> 
> RendererVk now has a private poolAllocator and VkAllocationCallbacks
> struct. The allocation callbacks are initialized to static functions
> in RendererVk::initializeDevice() and then passed to CommandPool init()
> and destroy() functions.
> 
> Using the pool allocator saves Command Pool/Buffer clean-up time which
> was showing us as a bottleneck is some cases.
> 
> Bug: angleproject:2951
> Change-Id: I81aa8a7ec60397676fa722d6435029db27947ef4
> Reviewed-on: https://chromium-review.googlesource.com/c/1409867
> Commit-Queue: Tobin Ehlis <tobine@google.com>
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>

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

Change-Id: I363a351667c4dddef79833061790da90de477e70
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:2951
Reviewed-on: https://chromium-review.googlesource.com/c/1430679Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Tobin Ehlis <tobine@google.com>