realtime_test: remove decoded frame count check

decoding is done if the decoder is available, with errors handled
accordingly. the encoded frame count should be sufficient for this test.

+ remove HandleDecodeResult() as it's redundant given the base
  implementation

BUG=webm:1233

Change-Id: I513c1c3475c58a746f4df627491bdc392fe21416
1 file changed