This implements the behavior discussed and specified here:
https://github.com/tc39/ecma262/issues/1461
https://github.com/tc39/ecma262/pull/1470

As part of making this change, I realized that we didn't actually
toggle the behavior between the optimized and unoptimized version
based on the --harmony-await-optimization flag at all and just the
unoptimized version by default.

This patch removes the unoptimized version and uses the optimized
version as the default.

The other builtins that use this flag are not touched as part of this
CL, they will be updated separately.

Bug: v8:8998
Change-Id: I315e1b39dda91d0127b5e567986485d713eaa78d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1525872
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60310}