Drive-by-cleanup: simplify related helper functions in CSA.

Bug: chromium:1022855
Change-Id: Icb15e6a35275708af313ec5776e92be4b6ce2524
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1910939
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64961}