[#317] api: Revert easyproto marshaler usage

It has caused a noticeable degradation in node.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

object/raw_test.go

@@ -303,6 +303,10 @@ func TestObjectEncoding(t *testing.T) {
 		o2 := New()
 		require.NoError(t, o2.UnmarshalJSON(data))
 
+		// New protobuf generator replaces nil payload with []byte{} in setters.
+		require.Empty(t, o2.Payload())
+		o2.SetPayload(nil)
+
 		require.Equal(t, o, o2)
 	})
 }