Revert "Refactor Update operation to return amount of input consumed."

This reverts commit 125febcb5d1888fa82e8c2eb307513598a537999.
diff --git a/google_keymaster_messages_test.cpp b/google_keymaster_messages_test.cpp
index 62a64d2..055cfa3 100644
--- a/google_keymaster_messages_test.cpp
+++ b/google_keymaster_messages_test.cpp
@@ -215,7 +215,7 @@
     msg.error = KM_ERROR_OK;
     msg.output.Reinitialize("foo", 3);
 
-    UniquePtr<UpdateOperationResponse> deserialized(round_trip(msg, 15));
+    UniquePtr<UpdateOperationResponse> deserialized(round_trip(msg, 11));
     EXPECT_EQ(KM_ERROR_OK, deserialized->error);
     EXPECT_EQ(3U, deserialized->output.available_read());
     EXPECT_EQ(0, memcmp(deserialized->output.peek_read(), "foo", 3));