Moving get_main_db out of tests and into superset utils (#5864)

tests/utils.py

@@ -7,20 +7,9 @@ from __future__ import unicode_literals
 import json
 from os import path
 
-from superset import db
-from superset.models import core as models
-
 FIXTURES_DIR = 'tests/fixtures'
 
 
 def load_fixture(fixture_file_name):
     with open(path.join(FIXTURES_DIR, fixture_file_name)) as fixture_file:
         return json.load(fixture_file)
-
-
-def get_main_database(session):
-    return (
-        db.session.query(models.Database)
-        .filter_by(database_name='main')
-        .first()
-    )