Patch to remove: https://gerrit.wikimedia.org/r/449022 Bug: https://phabricator.wikimedia.org/T200643

Commit message of patch copied here for your convenience:

Remove long-dead OutputPage methods set/getPageTitleActionText()

They were accidentally made non-functional in April 2009 by commit e4d21170. Subsequent commits 2d045fa1, 9e230f30, e275ea28, ae45908c removed all callers by October 2011. Needless to say, I found no callers in core or extensions.

It seems we have the functionality in some other way, probably just by directly calling setHTMLTitle(), so there's no need to revive this feature.