perf diff: Use __block_info__cmp() to replace block_pair_cmp()

'perf diff' uses block_pair_cmp() to compare two blocks. But
block_info__cmp() has the similar functionality and it's a bit more
complete.

This patch removes block_pair_cmp() and uses __block_info__cmp()
instead. __block_info__cmp() is wrapped by block_info__cmp() and it
doesn't receives a perf_hpp_fmt parameter.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200202141655.32053-3-yao.jin@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>