Revert "[MM-37013] Async job to fix CRT channel unreads (#18340)" (#19319)

This reverts commit 0da249c651.

model/migration.go

@@ -35,6 +35,5 @@ const (
 	MigrationKeyAddTestEmailAncillaryPermission        = "test_email_ancillary_permission"
 	MigrationKeyAddAboutSubsectionPermissions          = "about_subsection_permissions"
 	MigrationKeyAddIntegrationsSubsectionPermissions   = "integrations_subsection_permissions"
-	MigrationKeyFixCRTChannelUnreads                   = "fix_crt_channel_unreads"
 	MigrationKeyAddPlaybooksPermissions                = "playbooks_permissions"
 )