Change ARI to mention C++11, and remove some rules

Change ARI to mention C++11, and remove some rules

I noticed that ARI mentions "ISO C 90", but now gdb uses C++11.  This
patch updates some text to reflect this change.

I also noticed that a few rules can be removed now.  ARGSUSED doesn't
seem to be an issue any more (there's no code mentioning this and I
doubt most of us even remember this convention); PARAMS was specific
to K&R C; and __func__ is available in C++11.

gdb/ChangeLog
2019-07-19  Tom Tromey  <tromey@adacore.com>

	* contrib/ari/gdb_ari.sh: Mention C++11, not ISO C 90.
	(ARGSUSED, PARAMS, __func__): Remove rules.