Closed Issue: Diagrams generated by the Power tools add an error to the Error List [920]

Repro steps:
1. Create a basic model with one entity and one DbContext
2. Right click on the code file and select "View Entity Data Model (Read-only)" from EF context menu
3. When the diagram opens there is a new error in the error list:
Error 168: The provider did not return a ProviderManifest instance. Could not determine storage version; a valid storage connection or a version hint is required. C:\Users\lukew\AppData\Local\Temp\1\EntityContext.edmx 39 7 Miscellaneous Files

Note:
This error is only present while the .edmx file is open and disappears as soon as the file is closed again.
Under properties for the EDM in the designer, the connection string variable is empty
This error is NOT present when you generate the EDM XML with the power tools.

Comments: **EF Team Triage:** This isn't a significant problem as the preview is just a helpful read-only tool. Given that, we aren't going to try and fix this. If we have a significant number of complaints from customers we will reconsider (this issue was filed by a member of the EF team).