Check primary keys for all tables and drop ForeignReference (#21721)

Some dbs require that all tables have primary keys, see
- #16802
- #21086

We can add a test to keep it from being broken again.

Edit:

~Added missing primary key for `ForeignReference`~ Dropped the
`ForeignReference` table to satisfy the check, so it closes #21086.

More context can be found in comments.

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: zeripath <art27@cantab.net>

models/fixtures/foreign_reference.yml

@@ -1 +0,0 @@
-[] # empty