Remove use of mCanceled

It is possible for mCanceled to be set to true even though it
was canceled without ever playing back the cancelation message.
This can end up putting us in an incorrect state where the user
must release both fingers so ACTION_UP finally sets mCanceled to
false.

The cancel() method was still being called and since it does the
proper checks for removing/sending messages, the use of mCanceled
is unneccessary.

Change-Id: I38679d3bf65157a9ba5ca3d898c5c8d55e5df9f5
REF: LETTUCE-293