Revert part of "Fix: hurtling into wall of water"

Turns out this change to more accurately describe the wall of water in a
situation that shouldn't come up in-game messed up some uses of
dfeature_at which do a string comparison between the result and "pool of
water" to determine how to behave.

src/invent.c

@@ -4216,8 +4216,6 @@ dfeature_at(coordxy x, coordxy y, char *buf)
         cmap = S_lava; /* "molten lava" */
     else if (is_ice(x, y))
         dfeature = ice_descr(x, y, altbuf), cmap = -1; /* "ice" */
-    else if (IS_WATERWALL(ltyp))
-        dfeature = "wall of water";
     else if (is_pool(x, y))
         dfeature = "pool of water";
     else if (IS_SINK(ltyp))