stagefright: Don't enforce 16kHz rate for AMR-WB

This breaks android.media.cts.MediaRecorderTest#testRecordingAudioInRawFormats,
which tests specifically with 8kHz.

Change-Id: Ibfa54db4b2a82e502268be18f4ea405a41a88bfd
Merge branch 'cm-11.0' of git://github.com/CyanogenMod/android_frameworks_av into cm-11.0