perf hists browser: The dso can be obtained from popup_action->ms.map->dso

So no need to have a 'dso' member in 'popup_action', remove it as no
code is using it, already.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-76a6s0007slug0op0wkl6o8b@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>