Remove untestable, future-spec requirement.

The removed text dictates a requirement on future specifications which utilize
VCv2...not on VCv2 itself. So it is not testable with code against an implementation.

tests/5-advanced-concepts.js

@@ -166,17 +166,6 @@ describe('Advanced Concepts', function() {
         await assert.doesNotReject(endpoints.issue(
           require('./input/credential-evidences-ok.json')));
       });
-
-      // 5.10 Reserved Extension Points https://w3c.github.io/vc-data-model/#reserved-extension-points
-      it('In order to avoid collisions regarding how the following ' +
-        'properties are used, implementations MUST specify a type property ' +
-        'in the value associated with the reserved property.',
-      async function() {
-        this.test.link = `https://w3c.github.io/vc-data-model/#reserved-extension-points:~:text=In%20order%20to%20avoid%20collisions%20regarding%20how%20the%20following%20properties%20are%20used%2C%20implementations%20MUST%20specify%20a%20type%20property%20in%20the%20value%20associated%20with%20the%20reserved%20property.`;
-        // TODO: implement
-        this.test.cell.skipMessage = 'TBD';
-        this.skip();
-      });
     });
   }
 });