ChangeDocumentType does not fully remove vbaProject reference

**Description**

I'm using the sample code at https://docs.microsoft.com/en-us/office/open-xml/how-to-convert-a-word-processing-document-from-the-docm-to-the-docx-file-format to remove macros from a docm file and convert it to docx because we have some filtering software in place that prevents transferring files with macros.

Using that sample code I delete the VbaProjectPart, change the document type, and change the file extension. However, our filtering software identifies the resulting file as corrupt (Word 2016 opens the file just fine though, so it is probably within spec).

When I examine the contents of the .docx file, I notice that the [Content_Types].xml file at the root still contains the following line:
<Default ContentType="application/vnd.ms-office.vbaProject" Extension="bin"/>

The VbaProjectPart PartName reference is gone and no other content in the .docx file structure contains any macro components. I think that one line in [Content_Types].xml is enough to trip up our scanner.

Is there some other way to get rid of this line that I'm missing, is this a bug, or is this structure just something that our scanning software should accept?

**Information**

- .NET Target: .NET Core 2.1.12
- DocumentFormat.OpenXml Version: 2.10.0-beta0002

**Repro**

bool fileChanged = false;

using (WordprocessingDocument document = WordprocessingDocument.Open(sourcePath, true))
{
// Access the main document part.
var docPart = document.MainDocumentPart;

// Look for the vbaProject part. If it is there, delete it.
var vbaPart = docPart.VbaProjectPart;
if (vbaPart != null)
{
// Delete the vbaProject part and then save the document.
docPart.DeletePart(vbaPart);
docPart.Document.Save();

// Track that the document has been changed.
fileChanged = true;
}

// Change the document type to not macro-enabled
document.ChangeDocumentType(WordprocessingDocumentType.Document);
}

if (fileChanged)
{
// If it already exists, it will be deleted!
if (File.Exists(destinationPath))
{
File.Delete(destinationPath);
}

// Rename the file and save changes
Directory.CreateDirectory(destinationDirectory);
File.Move(sourcePath, destinationPath);
}

**Observed**

file.docx [Content_Types].xml still contains a macro reference.

**Expected**
file.docx should not contain any references to macros.