Volume Rocker: Hardcode music track seek option (1/2).

* The feature is enabled by default but not configurable.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>

PS2:

* Remove unneeded variables.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>

Change-Id: I0c72dd00f8a161255a59330862fa69c66735a3e4

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