Drop unused columns in sent_notifications

What does this MR do and why?

Drop unused columns in sent_notifications

These columns have already been ignored in the previous release

Migration output

main: == [advisory_lock_connection] object_id: 223660, pg_backend_pid: 45826
main: == 20230626070723 DropUnusedSentNotificationColumns: migrating ================
main: -- remove_column(:sent_notifications, :line_code)
main:    -> 0.0045s
main: -- remove_column(:sent_notifications, :note_type)
main:    -> 0.0005s
main: -- remove_column(:sent_notifications, :position)
main:    -> 0.0006s
main: == 20230626070723 DropUnusedSentNotificationColumns: migrated (0.0098s) =======
main: == [advisory_lock_connection] object_id: 223660, pg_backend_pid: 45826
ci: == [advisory_lock_connection] object_id: 223900, pg_backend_pid: 45828
ci: == 20230626070723 DropUnusedSentNotificationColumns: migrating ================
ci: -- remove_column(:sent_notifications, :line_code)
ci:    -> 0.0025s
ci: -- remove_column(:sent_notifications, :note_type)
ci:    -> 0.0003s
ci: -- remove_column(:sent_notifications, :position)
ci:    -> 0.0006s
ci: == 20230626070723 DropUnusedSentNotificationColumns: migrated (0.0127s) =======
ci: == [advisory_lock_connection] object_id: 223900, pg_backend_pid: 45828

main: == [advisory_lock_connection] object_id: 223220, pg_backend_pid: 46278
main: == 20230626070723 DropUnusedSentNotificationColumns: reverting ================
main: -- add_column(:sent_notifications, :line_code, :string)
main:    -> 0.0027s
main: -- add_column(:sent_notifications, :note_type, :string)
main:    -> 0.0008s
main: -- add_column(:sent_notifications, :position, :text)
main:    -> 0.0006s
main: == 20230626070723 DropUnusedSentNotificationColumns: reverted (0.0083s) =======
ci: == [advisory_lock_connection] object_id: 223160, pg_backend_pid: 46705
ci: == 20230626070723 DropUnusedSentNotificationColumns: reverting ================
ci: -- add_column(:sent_notifications, :line_code, :string)
ci:    -> 0.0017s
ci: -- add_column(:sent_notifications, :note_type, :string)
ci:    -> 0.0005s
ci: -- add_column(:sent_notifications, :position, :text)
ci:    -> 0.0004s
ci: == 20230626070723 DropUnusedSentNotificationColumns: reverted (0.0110s) =======
ci: == [advisory_lock_connection] object_id: 223160, pg_backend_pid: 46705

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #416155 (closed)