Revert "(Bug 44394) Add $wgGrownUpBehavior; enable ACUX only if true."

This reverts commit a715ad659a28f2b6d55c7bf3c5f77b7b5609d08f.

Change-Id: I84e425d70a22597483fb93cf674635ba88c02740
Merge "Revert "(Bug 44394) Add $wgGrownUpBehavior; enable ACUX only if true.""