remove the Document element from Edm lib

[xuzhg]

Issues

• See issue Add support for documentation to ODataConventionModelBuilder WebApi#26

Description

OData V3 spec has:

2.3 The edm:Documentation Element
The edm:Documentation element allows service authors to provide documentation for most model elements.
A model element MUST NOT contain more than one documentation element.
Refer to the [XML schema][csdl19] for details on which model elements support documentation.
A documentation element MUST contain zero or one edm:Summary and zero or one edm:LongDescription elements. The summary and long description elements MAY contain text that serves as the summary or long description. If both a summary and long description are provided, the summary MUST precede the long description.
For example:

<EntityType Name="Product"> 
 <Documentation>
  <Summary>Product names, suppliers, prices, and units in stock.</Summary>
  <LongDescription>...</LongDescription>
 </Documentation>
 ...
</EntityType>

However, that's not in OData Spec v4.

This PR is trying to remove the corresponding codes.

Checklist (Uncheck if it is not completed)

• Test cases added
• Build and test with one-click build and test script passed

Additional work necessary

If documentation update is needed, please add "Docs Needed" label to the issue and provide details about the required document change in the issue.

[mikepizzo]

Just to confirm; this is just code clean-up with no change to public surface area, right? I didn't see any change to public classes or to the api baseline file, but I just wanted to verify.

[xuzhg]

@mikepizzo Yes.