Remove unnecessarily overridden defaultEnterKeyStyle

The overriding defaultEnterKeyStyle was needed because there were two
Key's attributes to control key's visual, keyLabel and
keyIcon. Because these were merged into one keySpec attribute, there
is no need to override defaultEnterKeyStyle.

Bug: 16787857
Change-Id: I78ca2c7c9349e4532c67e8d6468a5b98309adc05