This reverts commit 4d45e7dc.

Reason for revert: Memory leak detected during roll in https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_asan_rel_ng/101750

Original change's description:
> Add FastVector for simple dynamic vector cases.
> 
> This optimized vector keeps an initial fixed size storage but has
> unbounded growth like a normal std::vector. It operates like a
> FixedVector initially but then switches the storage to an allocated
> pool when the element count exceeds the array limit.
> 
> This gives fast performance in the small case since no dynamic
> allocation is needed. It also handles the "slow" big case.
> 
> Bug: angleproject:2763
> Change-Id: I9c002b205bd4ac9fc171d1fdc42bc8ea5fe8dabe
> Reviewed-on: https://chromium-review.googlesource.com/1227794
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> Commit-Queue: Jamie Madill <jmadill@chromium.org>

TBR=ynovikov@chromium.org,jmadill@chromium.org,syoussefi@chromium.org

Change-Id: Iaec76244cc736a8469b80bfc8534fb0fd6c49e11
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:2763
Reviewed-on: https://chromium-review.googlesource.com/1232978Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>