meta: move relation.pk_column_id to table.pk_column_id

[erichanson]

Not everything in meta.relation has a primary key, because views, foreign tables, etc. do not have "real" primary keys. Remove meta.relation.primary_key_column_ids, and put it on meta.table instead. While we're at it, rename meta.column.relation_id to meta.column.table_id.