Delete a bunch of unused zephyr stuff

* Remove unused `ZSetFD`.
* Remove `__HM_set` which is never read.
* Remove `__Zephyr_open` global, which is redundant with `__Zephyr_fd != -1`.
* Remove `ZSetSrv.c`, as `ZSetServerState` is never called.
Consequently, remove `__Zephyr_server` global and all things that check it as it will never be TRUE.
* Remove zephyr internal debug code, as `ZSetDebug` is never called.
Also, make a couple debug messages go to libpurple.
* Remove unused `ZNewLocateUser` compatibility macro.

Testing Done:
Compile only.

Reviewed at https://reviews.imfreedom.org/r/249/