DXDocumentViewerView no longer used in c.documentviewer 5.x

[holdenhao]

An import to DXDocumentViewerView from c.documentviewer is in overrides.py. The class is no longer in version 5.x of the module so an import error occurs.

Also, the template for the override is no longer in the source code:

<configure package="collective.documentviewer" zcml:condition="installed collective.documentviewer">
    <browser:page
        ...
        template="templates/documentviewerdx.pt"
        ...