Disable building of dtudcfonted and dtudcexch

Disable building of dtudcfonted and dtudcexch

This software has a variety of problems, like including renamed X11
header files, and other nuttery.

These programs also have a very limited use, I doubt most people even
know what they are for or will miss them.

This commit prevents them from being built and installed.  If no-one
volunteers to get these into decent shape after the next release, they
will be removed from the repository.