[mlir] Remove an unused local variable (NFC) (#139351)

Author: kazutakahirata

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

@@ -2090,7 +2090,6 @@ void OpEmitter::genOptionalAttrRemovers() {
   // Generate methods for removing optional attributes, instead of having to
   // use the string interface. Enables better compile time verification.
   auto emitRemoveAttr = [&](StringRef name, bool useProperties) {
-    auto upperInitial = name.take_front().upper();
     auto *method = opClass.addInlineMethod("::mlir::Attribute",
                                            op.getRemoverName(name) + "Attr");
     if (!method)