Do not force DROP FUNCTION but rely on CREATE OR REPLACE

We'll bet on no old signature being left around.

Presence of an old signature would break at runtime
with a message like:
ERROR:  function CDB_UserTables() is not unique

Closes #25

scripts-available/CDB_Hexagon.sql

@@ -27,7 +27,7 @@ $$ LANGUAGE 'sql' IMMUTABLE STRICT;
 --               as the extent.
 --  
 --
-DROP FUNCTION IF EXISTS CDB_HexagonGrid(ext GEOMETRY, side FLOAT8);
+-- DROP FUNCTION IF EXISTS CDB_HexagonGrid(ext GEOMETRY, side FLOAT8);
 CREATE OR REPLACE FUNCTION CDB_HexagonGrid(ext GEOMETRY, side FLOAT8, origin GEOMETRY DEFAULT NULL)
 RETURNS SETOF GEOMETRY
 AS $$