How to permanently disconnect Visual Studio solution from source control

I have a Visual Studio 2012 solution with a few projects in it. Every time i open the solution file i get the message:

The mappings for the solution could not be found.
The active solution has been temporarily disconnected from source control because the server is unavailable. To attempt to reconnect to source control, close and then re-open the solution when the server is available. If you want to connect this solution to another server, use the Change Source Control dialog.

What i want to do is PERMANENTLY remove any mention of source control, but no luck so far.

Here is what i have tried so far

1. Deleted the usual suspect files, such as suo, mssccprj.scc, vssver.scc, etc
2. Manually opened every project file (.vbproj, .csproj) and deleted the four lines
   SccProjectName = "etc"
   SccAuxPath = "etc"
   SccLocalPath = "etc"
   SccProvider = "etc"
3. Ditto for the solution file
4. Noticed that there is a web site project (rather than web application project) in my solution, but being a website project i cannot perform step 2. on it.
5. Checked the dialog "File/Source Control/Advanced/Change Source Control" and noticed that every listed Solution/Projects have NO SERVER, NO BINDING, Status is "Not Controlled"

As well as the message described above (has been temporarily disconnected etc), the following 4 lines always get ADDED BACK to the solution file, no matter how many times i've deleted them.

SccProjectName = "MyApp"
SccAuxPath = "https://some.annoying.domain.com/VaultService"
SccLocalPath = "4~89a6b376-099d-49a7-801a-2ba7adb0e268"
SccProvider = "SourceGear Vault Visual Studio 2005 Client:{7BE9CE03-56BF-4682-9C06-78C68B134B30}"

These 4 lines are within the section that describes the website project.

Project("{E24C65DC-7377-472B-9ABA-BC803B73C61A}") = "MyApp",
"http://localhost/MyApp", "{A5301379-1092-419E-9B03-E37E16E0A8B2}"
ProjectSection(WebsiteProperties) = preProject

I strongly suspect it is the website project that is screwing it up. But where is the website project holding the source control info?

Further info:

I have already searched all file contents for the string "some.annoying.domain.com" but came up with nothing of significance (found in OTHER solutions, not this particular solution).

The solution appears to have been originally created in VS2010 (where the previous dev obviously used SourceGear's Vault product).

** NB: I could try to change the website proj to a web app proj, and see how it goes, but that's beside the point.

Change the source control plugin to None:

Tools -> Options -> Source Control -> Plug-in Selection: None

And respond with Yes to the question if you want the sources to not be under source control.