perf hists: Fix hists_evsel to release hists

Since hists__init doesn't set the destructor of hists_evsel (which is an
extended evsel structure), when hists_evsel is released, the extended
part of the hists_evsel is not deleted (note that the hists_evsel object
itself is freed).

This fixes it to add a destructor for hists__evsel and to set it up.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20151209021129.10245.28710.stgit@localhost.localdomain


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