Revert r44292 "Assign by ref to make sure cache fields carry over"

Revert r44292 "Assign by ref to make sure cache fields carry over"
This isn't PHP 4; the object's fields are changed on the object itself just fine. Unless people are changing the global variable $wgTitle to something different this should be fine. If there is a problem that this fixes, that's probably a problem itself and should be fixed in a cleaner way :D