command_util.sh: Make it read the function prototype from the source file

command_util.sh: Make it read the function prototype from the source file

This is much cleaner as the commands differ by gcc attribute usage,
e.g. __a_unused.  But it also means that in the source code

	(a) the opening bracket for the function body must not be on
	the same line (com_hist got this wrong),

	(b) for all command handlers, the parameters must be called
	fd, argc and argv,

	(c) If a command handler uses __noreturn, that attribute must
	be the first word, see audiod's com_term().

So change the few occasions where this was not the case.