fix(eventstore): cleanup org fields on remove (#8946)

# Which Problems Are Solved

When an org is removed, the corresponding fields are not deleted. This
creates issues, such as recreating a new org with the same verified
domain.

# How the Problems Are Solved

Remove the search fields by the org aggregate, instead of just setting
the removed state.

# Additional Changes

- Cleanup migration script that removed current stale fields.

# Additional Context

- Closes https://github.com/zitadel/zitadel/issues/8943
- Related to https://github.com/zitadel/zitadel/pull/8790

---------

Co-authored-by: Silvan <silvan.reusser@gmail.com>

cmd/setup/config.go

@@ -125,6 +125,7 @@ type Steps struct {
 	s36FillV2Milestones                     *FillV3Milestones
 	s37Apps7OIDConfigsBackChannelLogoutURI  *Apps7OIDConfigsBackChannelLogoutURI
 	s38BackChannelLogoutNotificationStart   *BackChannelLogoutNotificationStart
+	s39DeleteStaleOrgFields                 *DeleteStaleOrgFields
 }
 
 func MustNewSteps(v *viper.Viper) *Steps {