Revert biome rework (#38724)

* Revert "Fix world generation (#38713)"

This reverts commit 10fa6ff4af.

* Revert "Biome rework (#37735)"

This reverts commit fe7b96147c.

Content.Shared/Parallax/Biomes/Layers/IBiomeWorldLayer.cs

@@ -0,0 +1,12 @@
+namespace Content.Shared.Parallax.Biomes.Layers;
+
+/// <summary>
+/// Handles actual objects such as decals and entities.
+/// </summary>
+public partial interface IBiomeWorldLayer : IBiomeLayer
+{
+    /// <summary>
+    /// What tiles we're allowed to spawn on, real or biome.
+    /// </summary>
+    List<string> AllowedTiles { get; }
+}