Erase all traces of normal "generation" from fragment shaders
Remove the "feature" from the engine and default config
Remove any leftover documentation of it
Makes the liquid waving shader per-nodedef like waving leaves/plants,
instead of being applied to all liquids.
Like the waving leaves/plants shaders, the liquid waving shader can
also be applied to meshes and nodeboxes.
Derived from a PR by t0ny2.
