I would change query a little

select 'DROP PROCEDURE ['+ si.name + '].[' + so.name + ']'+ CHAR(13)+CHAR(10)+'GO'+CHAR(13)+CHAR(10)+

OBJECT_DEFINITION(object_id)+ CHAR(13)+CHAR(10)+'GO'+CHAR(13)+CHAR(10)

from sys.objects so inner join...