Revert "Fix warning: "unused variable 'attrClass'" (NFC)"

This reverts commit 724e6861b3.
This broke the build.

mlir/tools/mlir-tblgen/SPIRVUtilsGen.cpp

@@ -1144,6 +1144,7 @@ static bool emitSerializationFns(const RecordKeeper &recordKeeper,
       utilsString;
   raw_string_ostream dSerFn(dSerFnString), dDesFn(dDesFnString),
       serFn(serFnString), deserFn(deserFnString);
+  Record *attrClass = recordKeeper.getClass("Attr");
 
   // Emit the serialization and deserialization functions simultaneously.
   StringRef opVar("op");