Reverted _doc.py to Python 2-only version. Interim measure to prevent docs from failing during build, until all samples are updated with Python 2/3 compatibility.
Reverted _doc.py to Python 2-only version. Interim measure to prevent docs from failing during build, until all samples are updated with Python 2/3 compatibility.

opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv