fix(test): only test with callback

Author: BobTheBuidler

mypyc/test-data/run-weakref.test

@@ -10,13 +10,6 @@ class Object:
     """some random weakreffable object"""
     pass
 
-def test_weakref_ref():
-    obj = Object()
-    r = ref(obj)
-    assert r() is obj
-    obj = None
-    assert r() is None, r()
-
 def test_weakref_ref_with_callback():
     obj = Object()
     r = ref(obj, lambda x: x)