Fix black display inside opaque water

Opaque water's solidness was being set to 2, like a normal node.
When you swim, it is treated like a solid block, and the display
goes black.  Setting it to 1 like transparent water allows you to
see.

It looks somewhat awkward when you swim, look up, and see an opaque
wall of water (the surface), but there isn't much that can be done
about it.  If you made the water transparent so it looked good,
it would defeat the purpose :) .

src/nodedef.cpp

@@ -556,8 +556,6 @@ public:
 					f->solidness = 0;
 				} else {
 					f->solidness = 1;
-					if(f->alpha == 255)
-						f->solidness = 2;
 					f->backface_culling = false;
 				}
 				break;