CLIMATE-956 - Revert the changes in run_statistical_downscaling.py

- Some of the changes made by PR #444 have been reverted to make the codes work.
diff --git a/RCMES/statistical_downscaling/run_statistical_downscaling.py b/RCMES/statistical_downscaling/run_statistical_downscaling.py
index 62bc1a4..18b39fe 100644
--- a/RCMES/statistical_downscaling/run_statistical_downscaling.py
+++ b/RCMES/statistical_downscaling/run_statistical_downscaling.py
@@ -155,10 +155,16 @@
 
 print(downscale_option_names[DOWNSCALE_OPTION]+": Downscaling model output")
 
-xdownscale = [downscale.Delta_addition, downscale.Delta_correction, downscale.Quantile_mapping, downscale.Asynchronous_regression]
-if 0 < DOWNSCALE_OPTION <= len(xdownscale): xdownscale[DOWNSCALE_OPTION - 1]()
-else: sys.exit("DOWNSCALE_OPTION must be an integer between 1 and " + len(xdownscale))
-
+if DOWNSCALE_OPTION == 1:
+    downscaled_model_present, downscaled_model_future = downscale.Delta_addition()
+elif DOWNSCALE_OPTION == 2:
+    downscaled_model_present, downscaled_model_future = downscale.Delta_correction()
+elif DOWNSCALE_OPTION == 3:
+    downscaled_model_present, downscaled_model_future = downscale.Quantile_mapping()
+elif DOWNSCALE_OPTION == 4:
+    downscaled_model_present, downscaled_model_future = downscale.Asynchronous_regression()
+else:
+    sys.exit("DOWNSCALE_OPTION must be an integer between 1 and 4")
 
 """ Step 5: Create plots and spreadsheet """
 print("Plotting results")