DROP ROUTINE — remove a routine
DROP ROUTINE [ IF EXISTS ]name[ ( [ [argmode] [argname]argtype[, ...] ] ) ] [, ...] [ CASCADE | RESTRICT ]
   DROP ROUTINE removes the definition of an existing
   routine, which can be an aggregate function, a normal function, or a
   procedure.  See
   under DROP AGGREGATE, DROP FUNCTION,
   and DROP PROCEDURE for the description of the
   parameters, more examples, and further details.
  
   To drop the routine foo for type
   integer:
DROP ROUTINE foo(integer);
   This command will work independent of whether foo is an
   aggregate, function, or procedure.
  
This command conforms to the SQL standard, with these PostgreSQL extensions:
The standard only allows one routine to be dropped per command.
The IF EXISTS option
The ability to specify argument modes and names
Aggregate functions are an extension.
   Note that there is no CREATE ROUTINE command.