Remove 'Allow custom buttons' checkbox (1/2)

Let hardware buttons be rebound by default.

Change-Id: Ib4fcae7d93dc63d53490442d7ff44678583b0d9c

Conflicts:

	core/java/android/provider/Settings.java
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java

Conflicts:
	core/java/android/provider/Settings.java