Rewrite prior_biome_before_desertification

Delete most of the function.

src/sim_world_functions.py

@@ -104,43 +104,23 @@ def stoch_pro_lin(
 
     return s
 
-def prior_biome_before_desertification(current_biome, prob_not_desert, rng:np.random.Generator):
+def prior_biome_before_desertification(rng:np.random.Generator):
     """Returns the prior biome.
-    
-    Args:
-        current_biome: str. 
-        prob_not_desert: float. This is a number between
-            0 and 1 indicating the probability that the current
-            desert biome used to be another biome at the start
-            of the simulation.
 
     Returns:
         str. Indicates what the biome was historically.
     """
-    # If it's not desert now, then we do not
-    # worry about it being something else historically.
-    if current_biome != "Deserts & Xeric Shrublands":
-        past_biome = current_biome
-    else:
-        # We have a desert that could have been 
-        # something else.
-        r = rng.random()
-        if r <= prob_not_desert:
-            # It wasn't desert
-            other_biome_choices = [
-                "Tropical & Subtropical Grasslands, Savannas & Shrublands",
-                "Flooded Grasslands & Savannas",
-                "Temperate Grasslands, Savannas & Shrublands",
-                "Temperate Conifer Forests",
-                "Montane Grasslands & Shrublands",
-                "Temperate Broadleaf & Mixed Forests"
-            ]
-            past_biome = rng.choice(
-                a=other_biome_choices,
-                size=1
-            )
-        else:
-            # It has always been desert
-            past_biome = current_biome
-
+    other_biome_choices = [
+        "Tropical & Subtropical Grasslands, Savannas & Shrublands",
+        "Flooded Grasslands & Savannas",
+        "Temperate Grasslands, Savannas & Shrublands",
+        "Temperate Conifer Forests",
+        "Montane Grasslands & Shrublands",
+        "Temperate Broadleaf & Mixed Forests"
+    ]
+    past_biome = rng.choice(
+        a=other_biome_choices,
+        size=1
+    )[0]
+
     return past_biome