If we avoid throwing a stack overflow exception from Irregexp code during
direct calls, there is no need to construct exit frames before the Irregexp
call anymore. As that was the last remaining blocker, we can now implement the
entire stub in CSA.

BUG=v8:5339

Review-Url: https://codereview.chromium.org/2752143003
Cr-Commit-Position: refs/heads/master@{#44770}