Comment Cython (#3297)

Ultralytics REST API fix.

requirements.txt

@@ -25,6 +25,6 @@ pandas
 # scikit-learn==0.19.2  # for coreml quantization
 
 # extras --------------------------------------
-thop  # FLOPS computation
-Cython  # for pycocotools https://github.com/cocodataset/cocoapi/issues/172
+# Cython  # for pycocotools https://github.com/cocodataset/cocoapi/issues/172
 pycocotools>=2.0  # COCO mAP
+thop  # FLOPS computation