Reminder: drop owner_removed column on each projection

[muhlemmer]

The owner_removed column is legacy and was only kept around after #6083 on all projections in order to prevent migrating all of them at once, which could result in downtime. The new projection handlers already use a DELETE statement for owner removed events. Only entries that are older than v2.37 are kept around with owner_removed set to true.

This issue is a reminder for all devs, external and internal @zitadel/engineers:

When you are changing a projection, also drop the owner_removed column.

This way we can gradually migrate and cleanup old owner_removed = true entries.