gdb: remove uses of iterate_over_inferiors in remote-sim.c

gdb: remove uses of iterate_over_inferiors in remote-sim.c

This removes the two uses of iterate_over_inferiors, in favor of
range-based loops.

gdb/ChangeLog:

	* remote-sim.c (check_for_duplicate_sim_descriptor): Remove.
	(get_sim_inferior_data): Remove use of iterate_over_inferiors,
	replace with range-based for.
	(gdbsim_interrupt_inferior): Remove.
	(gdbsim_target::interrupt): Replace iterate_over_inferiors use
	with a range-based for.  Inline code from
	gdbsim_interrupt_inferior.