Kill off the option to not use RemoteControlClient.

In API level 18 the RCC will also be used for AVRCP 1.3 metadata, which
we certainly want to support. The decision whether to show the music
controls in the keyguard should be done at the framework level.

Change-Id: Ia17f9094231f3a76d1496ddf2ef2d90b2d4d9512