Explicitly delete the generator variable to make it clearer that it should not...

Explicitly delete the generator variable to make it clearer that it should not be used past that point.

PiperOrigin-RevId: 225423563

tensorflow/python/autograph/pyct/compiler.py

@@ -72,6 +72,7 @@ def ast_to_source(node, indentation='  '):
   # Reference cycles are quite disliked by TensorFlow's tests.
   if hasattr(generator, 'write'):
     generator.write = None
+  del generator
 
   return code