[mlir] add StringRef override for FunctionOpInterface::removeResultAttr (#129651)
A mirror of the corresponding overload for `removeArgAttr(unsigned
index, ::llvm::StringRef name)`
[here](https://github.com/llvm/llvm-project/blob/41473162fd886d7db548fb288cf3620570f73c17/mlir/include/mlir/Interfaces/FunctionInterfaces.td#L451-L454)