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.

Sponsored by: Netflix

grdc: Add copyright

Add the stock BSD copyright and license from the 4.4-Lite distribution
(indirected by SPDX).

Sponsored by: Netflix

grdc: add countdown timer mode

PR: 35113
Differential Revision: https://reviews.freebsd.org/D43463

Remove $FreeBSD$: one-line nroff pattern

Remove /^\.\\"\s*\$FreeBSD\$$\n/

grdc.6: Add an ENVIRONMENT section

- Add an ENVIRONMENT section

Obtained from: OpenBSD
MFC after: 5 days

Final step of eliminating the "games" distribution: Merge src/games
(or what's left of it, at least) into src/usr.bin.

This change will not be MFCed.

Discussed at: EuroBSDCon 2014
Committed from: EuroBSDCon 2015