FileBrowseField __init__ should not have a return statement

Let's say I have a model `FileModel` which has a `file` attribute which is a `FileBrowseField`. Now, `'file' in dir(FileModel)` will be `True`, however `hasattr(FileBrowseField, 'file')` will be 'False' and `getattr(FileBrowseField, 'file')` will raise an `AttributeError`. 

This behaviour is not consistent with Django model fields and can lead to unexpected problems when working with 3rd party libraries like Sphinx AutoDoc for example.