Remove untested sysv ipc support.

Resolves #680.

I know that shm doesn't work because we've stepped on it when X's MIT-SHM was accidentally enabled.  Looks like no one uses semaphores.  Phew!

We can add a new implementation of these, with tests, in the future if a need ever arises.  Should only take a few hours.  We would want to use the EmuFs to emulate the keyed shm segments.