All call sites passed nullptr as the isolate argument and DOUBLE as the
exponent type. Remove these unused arguments and related dead code.

Bug: v8:6666
Change-Id: Ie94d9b489f494b2a5c80f5cc3dc81013ed4f4414
Reviewed-on: https://chromium-review.googlesource.com/1006754Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52545}