command: remove radio commands

Remove these because I'm too lazy to convert them to proper
STREAM_CTRLs. Considering that probably nobody uses radio://, caring
about this is a complete waste of time. I will add these commands back
if someone asks for them, but I don't expect this to happen.
stream: remove stale MAX_STREAM_PROTOCOLS define
m_option.h: actually remove config.h include

This was supposed to be done in commit 80b34ebe.
ta: fix compilation with NDEBUG
options: use M_OPT_EXIT with -V

Otherwise, output will actually be muted during pre-pase stage, and it
will exit before running it again with output enabled.
player: replace some overlooked mp_msgs

There are still some using IDENTIFY, and some without context in
configfiles.c.
crosscompile-mingw.txt: fix instructions

The instructions hardcode some paths, so it sure would be better if the
listed commands actually use this path.
Rename getch2....c/h to terminal....c/h

"getch2" really tells nothing about what the heck this code does. It'd
be even worse when moving the rest of terminal handling code there.
terminal: move SIGTTOU signal handler setup code

This comes with a real change in behavior: now the signal handler is set
only when the terminal input code is active (e.g. not with
--no-consolecontrols), but this should be ok.