This flag was a leftover from very early Turbofan days and serves no
purpose. Non-OSR TF code automatically uses function context
specialization (FCS) when appropriate without looking at the flag
value. OSR TF code should never use FCS since it is cached by the
SharedFunctionInfo (not by the JSFunction).

Bug: v8:12161
Change-Id: Ifb5a10918dbdf34a7164f7e665a230698b793e9e
Fixed: chromium:1313419
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3571895
Auto-Submit: Jakob Linke <jgruber@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Linke <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79802}