Remove sockadapt layer from the VMS build.

Remove sockadapt layer from the VMS build.

SOCKETSHR is/was an interface to abstract out TCP/IP calls for the
various vendors' networking implementations, including the freeware
CMU-IP stack.  Neither SOCKETSHR nor CMU-IP has seen any maintenance
for over a decade and are likely not even C89-compliant.  The CRTL
socket routines have been supported by the different vendors' stacks
for many years so there is no reason to maintain an alternative, and
there probably hasn't been a real working alternative for some years
anyway.

The code is still there in maint-5.14 and earlier branches if
anyone has need of it.