Revert "[search] Remove more dead code"

Revert "[search] Remove more dead code"

This reverts commit 1525f6cd45e47c4e9623da234a1d55f862b39498.

This should be functionally equivilent to what was being done
before. When go is triggered but does not cause a redirect the
hook is called. Nothing is done with the result of the hook, same
as before.

Not going to bother deprecating, it doesn't particularly hurt the
architecture in any way, it was removed for being what appeared as dead
code due to a long removed feature. There are apparently a few usages of
this in extensions that may or may not work with recent releases of
mediawiki.

Bug: T160441
Change-Id: I368dec79431fbcc8d04f95afed8bbc7262a2e5de