toplevel: Eliminate reference to 'gui', 'libproc'

[Tom Tromey]

>>>>> "DJ" == DJ Delorie <dj@redhat.com> writes:

DJ> Technically OK, but could someone confirm the demise of gui and
DJ> libproc first?

`gui' was a gdb gui being written in scheme around 1995.
It died before Feb 1996.

Tom