Fix duplicated batch buffer test.

Two tests had the same code when the were
supposed to test different state.

PiperOrigin-RevId: 311149216

library/core/src/test/java/com/google/android/exoplayer2/mediacodec/BatchBufferTest.java

@@ -175,7 +175,7 @@ public final class BatchBufferTest {
 
   @Test
   public void batchWasConsumed_whenNotEmpty_isEmpty() {
-    fillBatchBuffer(batchBuffer);
+    batchBuffer.commitNextAccessUnit();
 
     batchBuffer.batchWasConsumed();