Remove documentation change not directly related to bugfix.

docs/ref/models/fields.txt

@@ -1343,12 +1343,12 @@ following optional arguments:
 .. attribute:: ImageField.height_field
 
     Name of a model field which will be auto-populated with the height of the
-    image each time the image attribute is set.
+    image each time the model instance is saved.
 
 .. attribute:: ImageField.width_field
 
     Name of a model field which will be auto-populated with the width of the
-    image each time the image attribute is set.
+    image each time the model instance is saved.
 
 Requires the `Pillow`_ library.
 
@@ -1367,6 +1367,7 @@ The default form widget for this field is a
     would always result in re-reading the file from the storage backend. If 
     your storage backend resizes images, the actual image's width and height 
     will not match the auto-populated fields.
+
 ``IntegerField``
 ----------------