Bug: 5105599
Don't clear slot data when slot is no longer in use.
The kernel will not resend absolute slot values if they are
unchanged, even if the slot was previously marked unused.
Because the protocol is stateful, this could cause problems if
evdev drops events (marked by SYN_DROPPED) since we cannot
query the initial values of the slots, but there's nothing
we can do.
Change-Id: Ie13e68097fb8ed2542c2f60338b499082cf9e77f
8bcbbefa3b