Prevent the tab key from double-tabbing

Tabbing from this field results in skipping ahead two fields.
The platform (TextView#dokeyDown()) catches the tab in onKeyDown(),
and we were catching it in onKeyUp(), causing it to be handled twice.

Everything seems to work as expected with this code removed.

Change-Id: I1386b374e93c8de2a9dfb4c57804222a2ad88002