db_column_table_primary fix

The query in this proc would return unwanted results such that a table would be returned even though the given column was not a primary key within that table. The updated query ensures that only a table where the given column is a primary key will be returned.
Just pointing out that I think constraint names are only unique within tables so we should probably join on table_name & constraint_name for completeness.

That said I don't think it is possible to have duplicate constraint_names for PRIMARY KEYS so probably not an issue here.

We can also use the "using" join condition which would mean that the output would only contain 1 column for "constraint_name" instead of 2.

```
SELECT table_name
FROM information_schema.table_constraints 
JOIN information_schema.constraint_column_usage using (table_name, constraint_name)
WHERE column_name=:column
AND constraint_type='PRIMARY KEY'
LIMIT 1;
```