InstallDocFormatter: Hyperlink Phabricator task numbers

Also removed the callback functions for the existing regexes. Nothing
has to be or is encoded or escaped at this time, so preg_replace()
can be used instead of preg_replace_callback().

Change-Id: I8cdddd602dcf7b67b8f2b06149b6a0859c70342c
Merge "InstallDocFormatter: Hyperlink Phabricator task numbers"