games/xnethack: fix wrong lua version

The game calls for lua 5.4, so USES=lua:54 when unbundling lua (PR #260224).

While we are at it:

• turn games/nethack-nox11 into flavor games/nethack@nox11
• simplify Makefile
• remove archaic pkg-deinstall.in; it's function is superseeded by messages pkg-deinstall(8) prints on its own

PR: 260224
Reported by: wesley.a.wroten@gmail.com