Refactor: tools: Remove stub versions of curses functions.

These functions were more useful when curses code was spread out across
more files and I didn't want to sprinkle CURSES_ENABLED everywhere.
Instead I could just specify it in one place and either the real
versions or the stub versions would get compiled, and everything else
would work fine.

This is no longer necessary since curses is confined to just one or two
places. Also, everywhere these functions are used is now also guarded
with CURSES_ENABLED.