Fix yolov3.yaml remove list (#6655)

Per https://github.com/ultralytics/yolov3/issues/1887#issuecomment-1041135181

models/hub/yolov3.yaml

@@ -28,7 +28,7 @@ backbone:
 # YOLOv3 head
 head:
   [[-1, 1, Bottleneck, [1024, False]],
-   [-1, 1, Conv, [512, [1, 1]]],
+   [-1, 1, Conv, [512, 1, 1]],
    [-1, 1, Conv, [1024, 3, 1]],
    [-1, 1, Conv, [512, 1, 1]],
    [-1, 1, Conv, [1024, 3, 1]],  # 15 (P5/32-large)