`#define` out water effect code for tiles that are entirely land.

`SHOW_REFLECTIVE_OCEAN` and `SHOW_OCEAN_WAVES` have moved into the `GlobeSurfaceShaderSet` so they can vary on a per-tile basis, rather than being set identically for all tiles.  Tiles that are entirely land now use `undefined` for their water mask texture instead of a shared "land" texture.

This is a roadmap item in #526.
I _hope_ the driver would optimize for this 1x1 case, but I would still go with `NEAREST` here.