SinaWeiboResourceOwner don't support OAuth2 revoke token
See details: http://open.weibo.com/wiki/API%E6%96%87%E6%A1%A3_V2/en#OAuth_2.0_API_.28Version_2_APIs_only_support_OAuth_2.0_authorization.29
Move default OAuth2 revoke code from GoogleResourceOwner to GenericOAuth2ResourceOwner