Water barrier cleanup required

[imagico]

Rendering of water barriers (dam, weir, lock_gate) is quite a mess at the moment with irritating and confusing discrepancies between queries, cartocss symbol code and labels.

Mapper consensus seems to be that

• waterway=dam can be mapped with either nodes, linear ways and polygons
• waterway=weir should be mapped with either nodes or linear ways
• waterway=lock_gate should be mapped with either nodes or linear ways

Hence the following changes should be made:

• remove label rendering for waterway=weir polygons - see here. This is unintended - hence a bug.
• remove waterway=weir and waterway=lock_gate from the water-barriers-poly layer query.