fix(torch): retinanet now trains correctly

Was actually fixed in #1265,
removed the exception in the export script

Author: Bycob

tools/torch/trace_torchvision.py

@@ -226,9 +226,8 @@ def get_detection_input():
                 elif "retinanet" in mname:
                     in_channels = model.backbone.out_channels
                     num_anchors = model.head.classification_head.num_anchors
-                    # replace pretrained head - does not work
-                    # model.head = M.detection.retinanet.RetinaNetHead(in_channels, num_anchors, args.num_classes)
-                    raise Exception("Retinanet with fixed number of classes is not yet supported")
+                    # replace pretrained head
+                    model.head = M.detection.retinanet.RetinaNetHead(in_channels, num_anchors, args.num_classes)
 
         detect_model = DetectionModel(model)
         detect_model.train()