OutputPage: addParserOutput*() family doesn't need to take a reference

We never assign to the variable, only call some (mutating) methods on
the object. With PHP 5 we don't need to pass this by reference.

The functions that evolved into this family were originally added in
r12337, back then we probably still ran on PHP 4 or something.

Change-Id: Ib4ab141ca6d803f9df0351b1f65c7e9955c37d57
Merge "OutputPage: addParserOutput*() family doesn't need to take a reference"