Drop objects in reverse order in downgrade script

Otherwise it fails downgrading, despite it is supposed to run everything
in the context of a transaction:

```
tests=# alter extension crankshaft update to '0.0.4';
ERROR:  cannot drop function cdb_pyaggs(numeric[],numeric[]) because
other objects depend on it
DETAIL:  extension crankshaft depends on function
cdb_pyaggs(numeric[],numeric[])
HINT:  Use DROP ... CASCADE to drop the dependent objects too.
```

release/crankshaft--0.1.0--0.0.4.sql

@@ -3,8 +3,6 @@
 -- Complain if script is sourced in psql, rather than via CREATE EXTENSION
 \echo Use "CREATE EXTENSION crankshaft" to load this file. \quit
 
---------------------------------------------------------------------------------
-
 -- Version number of the extension release
 CREATE OR REPLACE FUNCTION cdb_crankshaft_version()
 RETURNS text AS $$
@@ -13,43 +11,27 @@ $$ language 'sql' STABLE STRICT;
 
 --------------------------------------------------------------------------------
 
--- PyAgg stuff
-DROP FUNCTION CDB_PyAggS(Numeric[], Numeric[]);
-DROP AGGREGATE CDB_PyAgg(NUMERIC[]);
-
---------------------------------------------------------------------------------
-
--- Segmentation stuff
+-- Spatial Markov
 
 DROP FUNCTION
-  CDB_CreateAndPredictSegment(
-    target NUMERIC[],
-    features NUMERIC[],
-    target_features NUMERIC[],
-    target_ids NUMERIC[],
-    n_estimators INTEGER,
-    max_depth INTEGER,
-    subsample DOUBLE PRECISION,
-    learning_rate DOUBLE PRECISION,
-    min_samples_leaf INTEGER);
+  CDB_SpatialMarkovTrend (
+      subquery TEXT,
+      time_cols TEXT[],
+      num_classes INT,
+      w_type TEXT,
+      num_ngbrs INT,
+  	  permutations INT,
+  	  geom_col TEXT,
+  	  id_col TEXT);
 
-DROP FUNCTION
-  CDB_CreateAndPredictSegment (
-      query TEXT,
-      variable_name TEXT,
-      target_table TEXT,
-      n_estimators INTEGER,
-      max_depth INTEGER,
-      subsample DOUBLE PRECISION,
-      learning_rate DOUBLE PRECISION,
-      min_samples_leaf INTEGER);
 
 --------------------------------------------------------------------------------
 
 -- Spatial interpolation
 
 DROP FUNCTION CDB_SpatialInterpolation(
-    IN query text,
+    IN geomin geometry[],
+    IN colin numeric[],
     IN point geometry,
     IN method integer,
     IN p1 numeric,
@@ -57,8 +39,7 @@ DROP FUNCTION CDB_SpatialInterpolation(
     );
 
 DROP FUNCTION CDB_SpatialInterpolation(
-    IN geomin geometry[],
-    IN colin numeric[],
+    IN query text,
     IN point geometry,
     IN method integer,
     IN p1 numeric,
@@ -67,15 +48,34 @@ DROP FUNCTION CDB_SpatialInterpolation(
 
 --------------------------------------------------------------------------------
 
--- Spatial Markov
+-- Segmentation stuff
 
 DROP FUNCTION
-  CDB_SpatialMarkovTrend (
-      subquery TEXT,
-      time_cols TEXT[],
-      num_classes INT,
-      w_type TEXT,
-      num_ngbrs INT,
-  	  permutations INT,
-  	  geom_col TEXT,
-  	  id_col TEXT);
+  CDB_CreateAndPredictSegment (
+      query TEXT,
+      variable_name TEXT,
+      target_table TEXT,
+      n_estimators INTEGER,
+      max_depth INTEGER,
+      subsample DOUBLE PRECISION,
+      learning_rate DOUBLE PRECISION,
+      min_samples_leaf INTEGER);
+
+DROP FUNCTION
+  CDB_CreateAndPredictSegment(
+    target NUMERIC[],
+    features NUMERIC[],
+    target_features NUMERIC[],
+    target_ids NUMERIC[],
+    n_estimators INTEGER,
+    max_depth INTEGER,
+    subsample DOUBLE PRECISION,
+    learning_rate DOUBLE PRECISION,
+    min_samples_leaf INTEGER);
+
+--------------------------------------------------------------------------------
+
+-- PyAgg stuff
+
+DROP AGGREGATE CDB_PyAgg(NUMERIC[]);
+DROP FUNCTION CDB_PyAggS(Numeric[], Numeric[]);