This reverts commit b12ba06e.

Reason for revert:
After further discussion we decided to stick with fdlibm.

Original change's description:
> [builtins] stop using imprecise fdlibm pow
>
> This CL reinstates the old pow implementation which calls out to the
> system implementation of pow.
>
> Bug: v8:9622
> Change-Id: I3df997888ced3fb8b5bd4b810098e967649aaa55
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1774898
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Reviewed-by: Georg Neis <neis@chromium.org>
> Commit-Queue: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#66303}

TBR=yangguo@chromium.org,neis@chromium.org,hpayer@chromium.org,me@gus.host

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:9622
Change-Id: I941f70c7432cd2fab86e0eadcb2e1a9ec8195e91
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2072746
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66452}