wm: Nullify hardkey function assignments if enabling the navbar

This caused erroneous (and sometimes duplicate) events being generated
due to the regular key function assignments. The navbar does its
own action management, so don't try to derive from the actions
usually present in hard keys.

Change-Id: I82866e24547f8145cac4f07820ae90aacce09281
Merge "wm: Nullify hardkey function assignments if enabling the navbar" into cm-11.0