Update transform_instance_annotations to match the original function.
Update transform_instance_annotations to match the original function.

Summary:
update the transform_instance_annotations function to match the original version.
- The current version will cause troubles when training with person keypoints.

Reviewed By: alexander-kirillov

Differential Revision: D29870068

fbshipit-source-id: 5e41efbaef0632577821f28484c24132a2187a30

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2