perf jevents: Fix event code for events referencing std arch events

perf jevents: Fix event code for events referencing std arch events

The event code for events referencing std arch events is incorrectly
evaluated in json_events().

The issue is that je.event is evaluated properly from try_fixup(), but
later NULLified from the real_event() call, as "event" may be NULL.

Fix by setting "event" same je.event in try_fixup().

Also remove support for overwriting event code for events using std arch
events, as it is not used.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-By: Kajol Jain<kjain@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/1602170368-11892-1-git-send-email-john.garry@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>