ac definitions: update dataset configuration for instance-segmentation-person (#3176)

Author: eaidova

data/dataset_definitions.yml

@@ -159,7 +159,7 @@ datasets:
     annotation_conversion:
       converter: mscoco_mask_rcnn
       annotation_file: instances_val2017_persons.json
-      has_background: True
+      has_background: False
       sort_annotations: True
     annotation: mscoco_mask_rcnn_person.pickle
     dataset_meta: mscoco_mask_rcnn_person.json