When removing schema, type from previously selected schema are showing

[avernet]

Attach a schema A, close the dialog, reopen the dialog, change to another schema B, remove the schema, and notice that the types from schema A are listed and the button "delete existing schema" stays. This could be "by design", but it is confusing. Instead, at the end of the procedure above we should have no schema, and if users want to keep the schema that was selected before opening the dialog, they can click "cancel" in the dialog.