Enable building without ROS even if you have ROS

[henrygerardmoore]

I want to build without ROS enabled even though I have ROS2 installed. While following this guide, I found that in the current CMake, -DENABLE_ROS=OFF will be ignored if you have ROS2 installed (since it goes directly to ROS2.cmake instead of ROS1.cmake). This PR makes it so you can build without ROS if you so choose, even if you have it installed.

Please let me know if you need any further information or require changes :smile: