perf maps: Purge the entries from maps->names in __maps__purge()

No need to iterate via the ->names rbtree, as all the entries there
as in maps->entries as well, reuse __maps__purge() for that.

Doing it this way we can kill maps__for_each_entry_by_name(),
maps__for_each_entry_by_name_safe(), maps__{first,next}_by_name().

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-ps0nrio8pydyo23rr2s696ue@git.kernel.org


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