perf tools: Nuke unused map_groups__flush()

Since:

	9fdbf671 "perf tools: do not flush maps on COMM for perf report"

We have no users of this function, nuke it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Luigi Semenzato <semenzato@chromium.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-hsac1t42ehtva8gut8qe6hih@git.kernel.org


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