Move trusted-hosts.php artefact from wmf-config to extension repo

• There is no longer a need for the output path to be specified in the maintenance script.
• The extension now works out of the box.

• The $wgTrustedXffFile configuration is no longer used, and removed.
  
  Any existing setting of it will simply be ignored and thus not cause any errors.
  
  If a site admin has forked this repo or otherwise modified trusted-xff.txt, they will need to re-run generate.php while upgrading MediaWiki as their current copy in $IP/cache or elsewhere would no longer be applied

• Support for CDB is removed.

Bug: T212461
Change-Id: I6234c6a173e47b25a317a4fe7be66ec71b93f89a