debian:  Remove obsolete `libzmq4` build requirement
debian:  Remove obsolete `libzmq4` build requirement

The Dovetail Automata package repo shipped ZeroMQ v. 4 before Debian
Sid.  The upstream `libzmq3` package was based on ZeroMQ v. 3.
Anticipating upstream's future v. 4 package, the DA package was named
`libzmq4`.

However, the upstream package was never renamed, and a `libzmq3` v. 4
package now ships in Jessie.  The DA `libzmq4` package caused problems
upgrading distros, and so has been renamed to follow Debian.

This build requirement is now obsolete, since only the DA repo ever
had the `libzmq4` package, and it no longer does.

strahlex/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,kinsamanka/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,mhaberler/machinekit,mhaberler/machinekit,mhaberler/machinekit,strahlex/machinekit,araisrobo/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,ArcEye/MK-Qt5,mhaberler/machinekit,ArcEye/MK-Qt5,kinsamanka/machinekit,araisrobo/machinekit,araisrobo/machinekit,mhaberler/machinekit,araisrobo/machinekit,kinsamanka/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,mhaberler/machinekit,strahlex/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,ArcEye/MK-Qt5,araisrobo/machinekit,mhaberler/machinekit,strahlex/machinekit,araisrobo/machinekit,araisrobo/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,araisrobo/machinekit,mhaberler/machinekit,araisrobo/machinekit