The Response on Process Task isn't getting deleted as the response is used by one or more tasks
To delete the response we need to find the process tasks triggered with same response
select MIL_KEY from MIL where MIL_NAME='';
find the response which need to delete
select * from RSC where MIL_KEY ='1084';
find the process tasks triggered uses this response code
select * from OSI where RSC_KEY='' and MIL_KEY ='';
delete the process tasks which uses this response code.
delete from OSI where RSC_KEY='' and MIL_KEY ='';
Now login to design console
and delete the response you wanted to delete