Reverting in-development search changes pending fixing.

Reverting in-development search changes pending fixing.

Can we please do these sorts of experimental developments on branches before putting them to trunk? Our trunk is meant to be functional and ready to deploy at all times; doing experiments on trunk delays deployments because we have to test and fix them or roll them back.

Reverted:
r43376
r43385
r43403
r43404
r43405
r43406
r43423

Issues I noticed during a few minutes testing:
* Background color mismatch on the frameset for wikis that set a BG color on Special:
* 'browse pages with this prefix' is kind of funky in "Pages & Project" (goes to main namespace only)
* Which namespaces are in "Pages & Project" is not discoverable
* Default link to nonexistent help page Project:Searching kind of sucks. we should avoid doing those by default. It used to link to Help:Contents; any reason for the change from one page which might have previously existed to one which doesn't?
* "Create the page "Stuff" on this wiki!" - Double page creation links seem kind of weird. There should only be one, otherwise why have two?
* Bad prefix link output when search terms are not a valid wiki title
* We've lost the Whatlinkshere link from the old results