Fix the tap particles spilling out of the sink
This modifies the collision box so that the particles can go past the border and collide with the level where the drain is, but players don't intersect the mesh when they are on top of the sink.
Then, it sets
collision_remove on the particles. These two changes together, work around the Minetest issue reported in https://github.com/minetest/minetest/issues/2690 and make the particles work as expected.
Finally, it removes
node_box from the definition, as it doesn't seem to be used.