Fix a doctest

Author: kwankyu

src/sage/categories/primer.py

@@ -919,7 +919,6 @@ class SubcategoryMethods:
 to use Sage's introspection tools to recover where it's implemented::
 
     sage: x._repr_.__module__
-    'sage.structure.element_wrapper'
     sage: sage.misc.sageinspect.sage_getfile(x._repr_)
     '.../sage/structure/element_wrapper.pyx'