Mgv7: Always carve river channels in mountain terrain

Previously, rivers were sometimes blocked by vertical walls
of mountain terrain due to river carving being disabled
when base terrain height was below water_level - 16
Remove now unused base terrain heightmap created in
generateTerrain()

src/mapgen_v7.cpp

@@ -206,13 +206,15 @@ void MapgenV7::makeChunk(BlockMakeData *data)
 
 	blockseed = getBlockSeed2(full_node_min, seed);
 
-	// Generate terrain and ridges with initial heightmaps
+	// Generate base and mountain terrain
+	// An initial heightmap is no longer created here for use in generateRidgeTerrain()
 	s16 stone_surface_max_y = generateTerrain();
 
+	// Generate rivers
 	if (spflags & MGV7_RIDGES)
 		generateRidgeTerrain();
 
-	// Update heightmap to include mountain terrain
+	// Create heightmap
 	updateHeightmap(node_min, node_max);
 
 	// Init biome generator, place biome-specific nodes, and build biomemap
@@ -331,7 +333,6 @@ int MapgenV7::generateTerrain()
 	for (s16 z = node_min.Z; z <= node_max.Z; z++)
 	for (s16 x = node_min.X; x <= node_max.X; x++, index2d++) {
 		s16 surface_y = baseTerrainLevelFromMap(index2d);
-		heightmap[index2d] = surface_y;  // Create base terrain heightmap
 
 		if (surface_y > stone_surface_max_y)
 			stone_surface_max_y = surface_y;
@@ -382,9 +383,6 @@ void MapgenV7::generateRidgeTerrain()
 		for (s16 x = node_min.X; x <= node_max.X; x++, index++, vi++) {
 			int j = (z - node_min.Z) * csize.X + (x - node_min.X);
 
-			if (heightmap[j] < water_level - 16)  // Use base terrain heightmap
-				continue;
-
 			float uwatern = noise_ridge_uwater->result[j] * 2;
 			if (fabs(uwatern) > width)
 				continue;