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/migrate.go

@@ -83,13 +83,6 @@ func insertIssue(ctx context.Context, issue *issues_model.Issue) error {
 		}
 	}
 
-	if issue.ForeignReference != nil {
-		issue.ForeignReference.LocalIndex = issue.Index
-		if _, err := sess.Insert(issue.ForeignReference); err != nil {
-			return err
-		}
-	}
-
 	return nil
 }