Move combine over to statistics_counter_event.

Move combine over to statistics_counter_event.

Since we have statistics_counter_event now, combine should use that
instead of it is own custom printing of statistics.
The only thing that is not done any more after this patch is printing
out the total stats for the whole TU.

Note you need to use -fdump-rtl-combine-stats to get the stats in the combine
dump unlike before where the stats was dumped directly into the file.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	* combine.cc (dump_combine_stats): Remove.
	(dump_combine_total_stats): Remove.
	(total_attempts, total_merges, total_extras,
	total_successes): Remove.
	(combine_instructions): Don't increment total stats
	instead use statistics_counter_event.
	* dumpfile.cc (print_combine_total_stats): Remove.
	* dumpfile.h (print_combine_total_stats): Remove.
	(dump_combine_total_stats): Remove.
	* passes.cc (finish_optimization_passes):
	Don't call print_combine_total_stats.
	* rtl.h (dump_combine_total_stats): Remove.
	(dump_combine_stats): Remove.