Silence ARI for valid calls to abort

There are a handful of spots in gdb that validly call abort.  This
patch adds the appropriate ARI marker to these lines, to silence the
ARI report.  This also removes the "fix" call for "abort" from
gdb_ari.sh; it was incorrect and now is not needed.

gdb/ChangeLog
2019-12-13  Tom Tromey  <tromey@adacore.com>

	* contrib/ari/gdb_ari.sh: Remove "fix" call for abort.
	* utils.c (abort_with_message, dump_core, internal_vproblem): Add
	ARI marker to abort.
	* event-top.c (handle_sigsegv): Add ARI marker to abort.

Change-Id: I09ce6aa5010bbe4e5bb73ffdb727481be39d34d6