We no longer need this workaround. Also mCommandPoolFreeList dead code.

Bug: angleproject:3508
Change-Id: Ib73ddd431eb1bf9a55c3421111af4df5976cc1fb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2033485Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Tobin Ehlis <tobine@google.com>