TensorRT FP16 export with dynamic=True (ultralytics#7870)

Author: developer0hye

ultralytics/engine/exporter.py

@@ -227,7 +227,7 @@ def __call__(self, model=None):
         y = None
         for _ in range(2):
             y = model(im)  # dry runs
-        if self.args.half and (engine or onnx) and self.device.type != "cpu":
+        if self.args.half and onnx and self.device.type != "cpu":
             im, model = im.half(), model.half()  # to FP16
 
         # Filter warnings