The --type_info_threshold is no longer supported for a long time and
doesn't do anything useful nowadays, so no point in having that around.

Drive-by-fix: Remove the FeedbackVector::ComputeCounts() logic, since
it's dead code anyways by now.

Bug: v8:8834
Change-Id: I05f7517b3b82e34c0a83357337a456ab9c9f1f42
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1538128
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60442}