XML loaded courses should no longer be able to throw NoPathToItem.

The parent trees are built on a per-course basis (so it'll throw ItemNotFoundError
if an item exists in a different course from the one you're asking after. NoPathToItem
can still happen with MongoDB backed courseware. They store things like the info page
as HTML snippets which are orphaned from other content.

common/lib/xmodule/xmodule/modulestore/tests/test_modulestore.py

@@ -23,12 +23,3 @@ def check_path_to_location(modulestore):
     for location in not_found:
         assert_raises(ItemNotFoundError, path_to_location, modulestore, course_id, location)
 
-    # Since our test files are valid, there shouldn't be any
-    # elements with no path to them.  But we can look for them in
-    # another course.
-    no_path = (
-        "i4x://edX/simple/video/Lost_Video",
-        )
-    for location in no_path:
-        assert_raises(NoPathToItem, path_to_location, modulestore, course_id, location)
-