Docs - Ensure core models module level docstring does not appear in docs

Avoid the docstring being shared in the model reference documentation, this content is for core development only.
Update name of core modules.

docs/reference/models.md

@@ -1,10 +1,10 @@
 # Model reference
 
 ```{eval-rst}
-.. automodule:: wagtail.models
+.. module:: wagtail.models
 ```
 
-This document contains reference information for the model classes inside the `wagtailcore` module.
+This document contains reference information for the model classes inside the `wagtail.models` module.
 
 (page_model_ref)=