bpo-38210: Remove intersection operation with empty set

[corona10]

There was an unnecessary logic with the empty set.
The logic can be represented by blow code in pure python

result = set() # result = PySet_New(NULL);
it = iter(other)
result.intersection_update(other) 
# result will be empty set and iterator is fully consumed.
# so this logic should be removed

https://bugs.python.org/issue38210