Merge pull request #30 from lsst/u/fe/fix-202-3

Fix syntax error (deletion of unused variables, cell 13)

Author: MelissaGraham

DP1/200_Data_Products/202_Images/202_3_Difference_images.ipynb

@@ -336,7 +336,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "del ref, difference_image, x, y"
+    "del ref, difference_image"
    ]
   },
   {