Pass along tagFilter to ContribsPager, it already expects it

ContribsPager already has this below line:

    $this->tagFilter = isset( $options['tagfilter'] ) ? $options['tagfilter'] : false;

The reason the code already works fine is because, in ChangeTags.php, there's this fallback:

    if ( $filter_tag === false ) {
    	$filter_tag = $wgRequest->getVal( 'tagfilter' );
    }

Which essentially boils down to the same result as passing along tagfilter, which in
SpecialContributions is read from $wgRequest, passed to ContribsPager, and (well, currently
not) passed to ChangeTags

Change-Id: I12c0336ae31c5524e41fa0087afe2ba104dc7d37
Merge "Pass along tagFilter to ContribsPager, it already expects it"