BACKLOG-3653 - use VFSDataSource and remove old vfs implementation
https://jira.jahia.org/browse/BACKLOG-3653

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BACKLOG-3745 - When we unmount a folder from UI we need to remove the entries from jahia_external_provider_id and jahia_external_mapping
https://jira.jahia.org/browse/BACKLOG-3745

When a mount folder is deleted, delete the corresponding provider entry and identifier mappings