Bug 1139144 - Remove unused empty() definition from databuffer.h. r=mt

--HG--
extra : rebase_source : 4ea88ac04ef457fbbe3707e9e7d9af511e107688

media/mtransport/databuffer.h

@@ -36,7 +36,6 @@ class DataBuffer {
   const uint8_t *data() const { return data_.get(); }
   uint8_t *data() { return data_.get(); }
   size_t len() const { return len_; }
-  const bool empty() const { return len_ != 0; }
 
 private:
   UniquePtr<uint8_t[]> data_;