Remove ncollide3d usage

[repi]

Currently the physx crate uses ncollide3d for a couple of things, we should try and remove that usage as it feels unnecessary to bring in a different collision system in addition to physx.

[repi]

It is only this function that uses it in heightfield.rs so should be pretty easy to remove.

    /// Build the heightfield into a PhysX geometry and a trimesh we can use for rendering.
    pub fn build_with_trimesh(&self, cooking: &mut Cooking) -> (Geometry, TriMesh<f32>) {
        let heights = self.generate_heights();
        let heightfield_desc = self.create_desc(&heights);

        let vertices = self.generate_vertices(&heights);
        (
            cooking.create_heightfield(heightfield_desc, true),
            quad_with_vertices(&vertices[..], self.size.0, self.size.1),
        )
    }

[MaikKlein]

I talked to @tgolsson and this function is not used atm. Either we remove it or we triangulate it ourselves.

I'll nuke ncollide/nalgebra from the repo now.

[repi]

Sweet!

#22 is the issue of converting nalgebra to glam

[repi]

Fixed in #25