Remove low quality FunctionGraph test relying on stale pickle data

tests/gof/test_fg.py

-import os
 import pickle
 
-import pytest
-
-import theano
-from theano.compat import PY3
-from theano.gof.fg import FunctionGraph
 from theano import tensor as tt
+from theano.gof.fg import FunctionGraph
 
 
 class TestFunctionGraph:
@@ -16,24 +11,3 @@ class TestFunctionGraph:
 
         s = pickle.dumps(func)
         pickle.loads(s)
-
-    @pytest.mark.skipif(
-        not theano.config.cxx, reason="G++ not available, so we need to skip this test."
-    )
-    @pytest.mark.slow
-    def test_node_outputs_not_used(self):
-        # In the past, we where removing some not used variable from
-        # fgraph.variables event if the apply had other output used in
-        # the graph. This caused a crash.
-        # This test run the pickle that reproduce this case.
-        with open(
-            os.path.join(os.path.dirname(__file__), "test_fg_old_crash.pkl"), "rb"
-        ) as f:
-            from theano.misc.pkl_utils import CompatUnpickler
-
-            if PY3:
-                u = CompatUnpickler(f, encoding="latin1")
-            else:
-                u = CompatUnpickler(f)
-            d = u.load()
-        f = theano.function(**d)