Replace use of &$this

Replace use of &$this

Use of &$this doesn't work in PHP 7.1. For callbacks to methods like
array_map() it's completely unnecessary, while for hooks we still need
to pass a reference and so we need to copy $this into a local variable.

Bug: T153505
Change-Id: I8bbb26e248cd6f213fd0e7460d6d6935a3f9e468