HID: magicmouse: remove timestamp logic

The timestamps from the device are currently stored in the private data
structure. These aren't used, so remove them. I've left a comment
detailing the protocol for future reference.

Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Acked-by: Michael Poole <mdpoole@troilus.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>