- remove redundant checks
- use switch over PromiseHookType

Change-Id: I89a5328009634a7025feb77e22334773c2886868
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2224225Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68210}