fix: join on bucket_id column

- For queries that want to join on
bucket_id column, we had wrong logic
of removing that column from child scan,
now if we have bucket_id column in
join we won't delete bucket_id from scan
node.
- Fix conflict resolution for join on
bucket_id: if we see that join is done
on bucket_id, we don't need any motions.

Note: there is still a problem when we don't
use "bucket_id" in join condition:

select t1."bucket_id", t2."bucket_id" from t1
join t2 on ...

This query will fail with error that it can't
find "bucket_id" column.