Ref T13395. I want to merge libphutil into Arcanist ("the client part") and Phabricator ("the server part") since modern libphutil doesn't provide much value being standalone but makes verison management and deployment more complicated.

In service of this goal, remove a large number of classes which are only used at the web application level (by Phabricator) out of libphutil. The next change moves them into "phabricator/".

Grepped for all (?) affected symbols in libphutil and Arcanist, found no callsites.