[media] rc-rc6-mce: minor keymap updates

Microsoft's Windows Media Center specification and requirements doc from
2011.03.18 now refers to the former Power Toggle button as the Sleep
Toggle, and recommends using a new moon sleep icon for it. Its the same
key, but its apparently always been meant to put the system to sleep,
not power it off. Adjust accordingly. While we're here, lets also remove
the duplicate KEY_PLAYPAUSE entry.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>