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

Let hardware buttons be rebound by default.

Change-Id: If19fb357cf9dcea419bea6242f4fc1f388916e4d

Conflicts:

	res/values-ca/cm_strings.xml
	res/values-de/cm_strings.xml
	res/values-es/cm_strings.xml
	res/values-it/cm_strings.xml
	res/values-lt/cm_strings.xml
	res/values-nl/cm_strings.xml
	res/values-pl/cm_strings.xml
	res/values-pt/cm_strings.xml
	res/values-ru/cm_strings.xml
	res/values-th/cm_strings.xml
	res/xml/button_settings.xml