[wip/talos-pal-hardware-gazebo] Fix Makefile

Drop useless CMAKE_PREFIX_PATH definition, as well as the $(info)
statement. cmake does not care about ROBOTPKG_BASE, since this is just the
location of the robotpkg_* tools, and the $(info) will trigger strange failures
in internal scripts that parse the output of some robotpkg targets.

Also fix PKGREVISION, no _.