thinkpad-acpi: drop HKEY event 0x5010

HKEY event 0x5010 is useless to us: old ThinkPads don't issue it.  Newer
ThinkPads won't issue it anymore.  And all ThinkPads issue 0x1010 and
0x1011 events.

Just silently drop it instead of sending it to userspace.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>