Fix stray `pretrained=True` warnings from torchvision (#1346)
Summary:
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1346
Follow up to #1280, this fixes vision_maskrcnn and Super_SloMo which use torchvision, but do not subclass TorchVisionModel. This fixes the warning about `pretrained=True` being a deprecated option.
Test Plan: Imported from OSS
Reviewed By: xuzhao9
Differential Revision: D42053509
Pulled By: davidberard98
fbshipit-source-id: 5ddaab0c4a4a21dc1680f890f50504101271a2da
