Eliminate redundant f= and t= parameters from board urls

I noticed that Google (and probably other search engines), do not index phpBB forums using the canonical urls which are provided in each page. I presume that this is because all of the links to phpBB forums (internal and external) generally have redundent parameters (f= and/or t=) in the url.

Following up on https://area51.phpbb.com/phpBB/viewtopic.php?f=108&t=45551&start=40

I have created a patch which eliminates all of the redundant parameters, and tidies up a couple of places where the redundant parameters were actually used. I believe that allowing the use of these parameters (which may be externally manipulated) poses a potential security risk.