perf map: Remove needless struct forward declarations

At some point we may have needed that, not anymore.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-hnao13231bsl7xml5wn8h4iu@git.kernel.org


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