perf script: Fix memory 'threads' and 'cpus' leaks on exit

ASan reports several memory leaks while running:

  # perf test "82: Use vfs_getname probe to get syscall args filenames"

Two of these are caused by some refcounts not being decreased on
perf-script exit, namely script.threads and script.cpus.

This patch adds the missing __put calls in a new perf_script__exit
function, which is called at the end of cmd_script.

This patch concludes the fixes of all remaining memory leaks in perf
test "82: Use vfs_getname probe to get syscall args filenames".

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Fixes: cfc8874a

 ("perf script: Process cpu/threads maps")
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/5ee73b19791c6fa9d24c4d57f4ac1a23609400d7.1626343282.git.rickyman7@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>