RIP out mongo

Since sqlalchemy is providing our database abstraction and we have
moved away from Mongo as the underlying database, it is now time to
simplify things and rip out mongo. This provides the bulk of the
changes, and can stand on its own. There are some followup tasks
that can be done, such as removing now unneeded abstraction layers,
e.g. db.sql.fake.py

mediagoblin/init/__init__.py

@@ -66,15 +66,13 @@ def setup_database():
     load_models(app_config)
 
     # Set up the database
-    connection, db = setup_connection_and_db_from_config(app_config)
+    db = setup_connection_and_db_from_config(app_config)
 
     check_db_migrations_current(db)
 
-    setup_globals(
-        db_connection=connection,
-        database=db)
+    setup_globals(database=db)
 
-    return connection, db
+    return db
 
 
 def get_jinja_loader(user_template_path=None, current_theme=None,