Issue title: Still support rfcn?
 Issue body: It seems rfcn has been removed to another code file,and I cannot find any trained model or model config file in this repro to re-produce rfcn?Could you provide more details about this part?Thanks
 Comments: 
 Comment 0: Any response
 Comment 1: I also want to know if there is any plan for rfcn? Thanks.
{'source': 'GithubIssues', 'repo_name_with_owner': 'open-mmlab/mmdetection', 'issue_id': 486419840, 'repo_stars': 21946.0}