Revert "grdc: Add copyright"

It turns out this wasn't in 4.4BSD. I had a false positive for gdc.c
(which is in 4.4BSD, but part of gated, not this). gdc.c comes from the
ncurses tests, so it shouldn't have this copyright. This version is
mostly Amos Shapir and John Lupien's code. It comes from ncurses test
directory. ncurses has made dozens of improvements to this file since
we imported it in 1997 (which pre-dates their online history), so it's
not clear if their new copyright applies (which doesn't mention Amos
or John) or if some other copyright applies. In any case, it wasn't
4.4BSD, so revert this.

This reverts commit 6ed7d0e3ac9c34fa9deeb73f2322b9f25b708788.

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