Fix ERD delete crash on stale foreign key column. #8318 (#10042)

removeOneToManyLink looked up a column by the FK's stored local_column
name and read .attnum unconditionally. After a column rename the stored
name no longer matches, so _.find returned undefined and .attnum threw,
blocking deletion of the table/link. Use optional chaining so a stale FK
simply doesn't match the link being removed and deletion proceeds.