Python: Add copy of extractor tests

These get to live next to the existing library and query tests, and are
run as part of both the Python 2 and Python 3 language tests.

python/ql/test/extractor-tests/pruning/plurally_dead_edges.py

@@ -0,0 +1,17 @@
+# -*- coding: utf-8 -*-
+
+#
+
+class Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx(Yyyyyyyyyyyyyyyyyyyyyyyy):
+
+
+    def ffffffffffffffffffffffff(self, p, ppppppp=20):
+
+        debug = False  # True
+        if debug:
+            print("Some text")
+        if debug:
+            #With splitting, the edge to the print is dead for two different reasons.
+            #But we can only delete it once.
+            print("Some more text")
+        f = 1