Suggest changing *x to x in toplevel_ref_arg

[llogiq]

If we have a toplevel ref argument, toplevel_ref_arg will suggest removing the ref (it should perhaps also propose removing mut if it's there). However, this will lead to error if the argument is dereferenced within the function.

At the very least, the message should note that dereferences can lead to errors. Better yet would be to find all those instances and suggest removing the *.