perf trace: Free malloc'd trace fields on exit

ASan reports several memory leaks running:

  # perf test "88: Check open filename arg using perf trace + vfs_getname"

The first of these leaks is related to struct trace fields never being
deallocated.

This patch adds the function trace__exit, which is called at the end of
cmd_trace, replacing the existing deallocation, which is now moved
inside the new function.

This function deallocates:

 - ev_qualifier
 - ev_qualifier_ids.entries
 - syscalls.table
 - sctbl
 - perfconfig_events

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
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/de5945ed5c0cb882cbfa3268567d0bff460ff016.1626343282.git.rickyman7@gmail.com
[ Removed needless initialization to zero, missing named initializers are zeroed by the compiler ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>