[flang][NFC] Remove unused variable

Author: clementval

flang/lib/Lower/OpenACC.cpp

@@ -898,7 +898,7 @@ static void genACC(Fortran::lower::AbstractConverter &converter,
   const auto &accClauseList =
       std::get<Fortran::parser::AccClauseList>(waitConstruct.t);
 
-  mlir::Value ifCond, asyncOperand, waitDevnum, async;
+  mlir::Value ifCond, waitDevnum, async;
   SmallVector<mlir::Value> waitOperands;
 
   // Async clause have optional values but can be present with