This wasn't actually hooked up any more, so it was pretty much
all dead code. The handling of this in the command line options
is gone.
In `bin/makefile-tail`, `DEVFILES` and `LIBFILES` became identical, so
`DEVFILES` went away.
CLX is a Common Lisp implementation of the X client library.
It has some code in C, which was present here as `src/socket.c`
and `src/socdvr.c`, exposed via opcodes in `src/subr.c`. This code
had been removed (with prejudice apparently) by commenting out
the code in `src/subr.c` with `#if NEVER`.
This code would've been used by the Medley system images, but
that code doesn't appear to be present. (There may or may not
be something related in `XMAS` in the Medley repository.)
