Revert of [regexp] Add stub for RegExpExec instead of inlining (patchset #1 id:1 of https://codereview.chromium.org/2677073004/ )

Reason for revert:
Doesn't fix perf regressions in crbug.com/688972 and introduces new ones for RegExp in crbug.com/689395.

Original issue's description:
> [regexp] Add stub for RegExpExec instead of inlining
>
> The code produced for RegExpExec is quite large, and we ended up completely
> inlining it several spots.  This CL moves RegExpPrototypeExecBody into two
> stubs (one each for fast and slow paths) and converts inlined uses into stub
> calls. This decreases the local x64 snapshot size by around 80K.
>
> BUG=chromium:688972
>
> Review-Url: https://codereview.chromium.org/2677073004
> Cr-Commit-Position: refs/heads/master@{#42965}
> Committed: https://chromium.googlesource.com/v8/v8/+/5ea144afe3fd98896fc097a3523de9ab0cb8cd61

TBR=yangguo@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:688972

Review-Url: https://codereview.chromium.org/2679063003
Cr-Commit-Position: refs/heads/master@{#42985}