rP16751 removed the ability for terrain to affect movement speed. The JPS pathfinder cannot support it, and the approach was poor anyways.
This lets us remove the dependency on CTerrainTextureManager everywhere.
Also update XML (!this can break mods because of RelaxNG change).
A better approach would be to define a 2D map of terrain speed multipliers and let map-makers customize that, either by matching with textures or by painting it manually. This is more flexible, would be simulation-only, and would be a simpler implementation overall.