This only works when shaders are enabled.
The centroid varying avoids that the textures (which repeat themselves out of bounds) are sampled out of bounds in MSAA.
If MSAA (called FSAA in minetest) is disabled, the centroid keyword does nothing.
Erase all traces of normal "generation" from fragment shaders
Remove the "feature" from the engine and default config
Remove any leftover documentation of it
