pc-select-map shadows the work of init-post-mswindows-win for (shift
delete), (shift insert), and (control insert) with the older, x- names.
This is okay for x-kill-primary-selection and x-copy-primary-selection,
which are just obsolete aliases.
But yank-clipboard-selection now only does x-yank-clipboard-selection in
the x device-type case. On NT4, one gets an undefined function.
Unless I'm missing something, it's just a matter of removing the x-'s from
these three top-level bindings in pc-select.el.