Make all GNUstep ports install into the System domain so that the Local domain is available for stuff built from source.
Some ports were already installing in the System domain, for these just remove the Makefile lines explicitly specifying the install domain.
The rest are installed in the Local domain, remove any overrides, update their pkg-plists and any explicit paths in the Makefiles and then bump port revision.
Approved by: bapt (mentor)
Differential Revision: https://reviews.freebsd.org/D2977