That flag has been enabled by default for well over a year (March 25, 2022) in 248874@main. It's now outlived its purpose so we should remove it.
Pull request: https://github.com/WebKit/WebKit/pull/19274
Committed 269517@main (9c2a7feebac7): <https://commits.webkit.org/269517@main> Reviewed commits have been landed. Closing PR #19274 and removing active labels.
<rdar://problem/117200574>