How to remove mount point for defunct Google Drive external storage

Nextcloud version (eg, 20.0.5): 20.0.8
Operating system and version (eg, Ubuntu 20.04): Debian 10.8
Apache or nginx version (eg, Apache 2.4.25): Apache/2.4.38 (Debian)
PHP version (eg, 7.4): 7.4

After upgrading to Nextcloud 20.0.8, I removed the old and defunct Google Drive external storage provider. Unfortunately the stale mount point is still there for myself and my admin user. The mount point cannot be deleted. Trying to do so yields error message "Error when deleting ", approximately (the German message is: Fehler beim Löschen der Datei “GoogleDrive”.)

The existence of the stale mount point hinders the nextcloud desktop client from syncing the files: “A Http transmission error happened. The server file discovery is missing data”

How can I remove the mountpoint?

I found the solution myself: open data/owncloud.db and delete the conflicting entries from the oc_external_mounts table. I did some cleanup in oc_storages and oc_external_config as well.