Switch dungeon type detection to biome name

see #2400, also removed a now unused alias

mods/default/mapgen.lua

@@ -35,7 +35,6 @@ minetest.register_alias("mapgen_cobble", "default:cobble")
 minetest.register_alias("mapgen_stair_cobble", "stairs:stair_cobble")
 minetest.register_alias("mapgen_mossycobble", "default:mossycobble")
 minetest.register_alias("mapgen_stair_desert_stone", "stairs:stair_desert_stone")
-minetest.register_alias("mapgen_sandstonebrick", "default:sandstonebrick")
 
 
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