stagefright: Fix the unhappy path in ACodec configuration step

 * CTS is very unhappy that ACodec's unhappy path is not taken
   when MediaCodec sends some very unhappy configuration. Like
   trying to use a decoder to encode. Nobody is happy with this.
 * Remove a check left over from 12.0 which is no longer needed
   to make the test happy.
 * Overall, on a scale of 0 (unhappy) to 10 (happy), I would rate
   my CTS experience of MR1 as a 7.

Change-Id: Ia798642e0fe0fed0bb1156328adb4c5bd9acf9c4