Problem: --with-libzmq-include-dir and -lib-dir were broken

* --with-libzmq-include-dir went and added /include once more, which
  is obviously broken (it should point straight to the directory that
  holds zmq.h)

* --with-libzmq-lib-dir did nothing except add itself to the help
  output, and confuse users.

Solution: remove both these, which are redundant with --with-libzmq.