[flang] Fix characterization of result of function returning procedur… (#66248)

…e pointer

The procedure characterization package correctly characterizes the
result of a reference to a function that returns a procedure pointer. In
the event of a result that is a pointer to a function that itself is a
procedure pointer, the code in pointer assignment semantics checking was
mistakenly using that result's procedure characteristics as the
characteristics of the original function reference. This is just wrong;
delete it.