Make solid water behave more consistently

The "water" terrain (as used on the Plane of Water) behaved
strangely outside the plane. Make it behave a bit more consistently,
although it's still not really usable elsewhere.

The rationale here being it's a solid wall of water.

Firstly, disable levitation and flying (which was already done
when moving into the water on the Plane of Water), and moving into
it refers to it as a "wall of water" to make it clear it's a solid
block of water.

src/hack.c

@@ -2263,7 +2263,7 @@ switch_terrain(void)
 {
     struct rm *lev = &levl[u.ux][u.uy];
     boolean blocklev = (IS_ROCK(lev->typ) || closed_door(u.ux, u.uy)
-                        || (Is_waterlevel(&u.uz) && lev->typ == WATER)),
+                        || lev->typ == WATER),
             was_levitating = !!Levitation, was_flying = !!Flying;
 
     if (blocklev) {