Support removal of datasource from mapping

Description

1. Install an MA connector.
2. Configure it.
3. Edit a form
4. On the *Mapping *tab, select a Datasource.

Expected
The UI provides a "Reset" or "Clear" button to reset the "Connect to Datasource" field.

Actual
There is no way to go back. The UI should provide a "Reset" or "Clear" button to reset the "Connect to Datasource" field if a customer no longer wants to send to the connector.