[2.0 bugs] unittest_manager ast_from_class tests

Originally reported by: **BitBucket: [ceridwenv](http://bitbucket.org/ceridwenv), GitHub: @ceridwen**

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This method is now redundant, given the ast_from_class function in raw_building. Should I move these tests to unittest_raw_building? If so, the API is different: Manager.ast_from_class always returns a ClassDef node that is the child of whatever module it's in, while raw_building.ast_from_class returns only the class itself. Should I just write new tests?

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- Bitbucket: https://bitbucket.org/logilab/astroid/issue/253

Inspect the tests in unittest_manager and compare their Manager.ast_from_class expectations with raw_building.ast_from_class. Check unittest_raw_building and run the relevant test files before deciding whether to move or rewrite the cases. Done means the redundant coverage is removed or relocated, the API differences are covered, and the test suite passes.

Written by the indexing model from the issue text.