Explicitly use Python3 in shebang for teleop nodes

[jyang-cpr]

It appears that catkin_python_install() is not working correctly in terms of selecting Python3 at runtime to run the teleop.py and teleop_speed_control.py, when the package is installed from deb/binary or with catkin_make install. This can be reproduced on a Noetic machine (e.g. my laptop and 2 Jackals) with:

sudo apt-get update sudo apt-get install ros-noetic-axis-camera rosrun axis_camera teleop.py

OR

cd ~/catkin_ws/src git clone -b noetic-devel https://github.com/ros-drivers/axis_camera.git cd .. catkin_make install source install/setup.bash rosrun axis_camera teleop.py

In both instances, ROS will complain with /opt/ros/noetic/bin/rosrun: /home/jyang/projects/test_ws/install/lib/axis_camera/teleop.py: /usr/bin/python: bad interpreter: No such file or directory

To fix this, we can just specify Python3 in the shebang.

This PR also removes the shebang in setup.py, since it is not necessary, as per:

• http://docs.ros.org/en/jade/api/catkin/html/howto/format2/installing_python.html
• https://stackoverflow.com/questions/35701131/why-does-setup-py-usually-not-have-a-shebang-line#:~:text=setup.py%20is%20going%20to,with%20the%20interpreter%20before%20it.