Putting an early exit if statement at the top instead of wrapping the
whole file contents unbreaks unit test configs, as was discovered for
SysId. It reduces nesting as well.
Unused plugins were removed from the beginnings of files as well.
It was only being used for fs::remove() (added in #3463), which is easily
replaced by std::remove().
The code change does not affect the WPILib tools, as this code is not used when JSON save files are used.
These hide the platform specifics behind a common C++ API. Platforms:
- Windows: DirectX 11 (with 10 backwards compatibility)
- Linux: OpenGL 3
- Mac: Metal
