ui: drop altgr and altgr_r QKeyCodes

The right alt key (alt_r aka KEY_RIGHTALT) is used for AltGr.
The altgr and altgr_r keys simply don't exist.  Drop them.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20170727104720.30061-1-kraxel@redhat.com