Hi Tufail
There is not straight standard function to do what you are trying to do. I've just explained why SU10 didn't remove the roles for you
As Julius has mentioned there are BAPIs but you would need to do development. I've written an ECATT before to loop through SU10 to remove (1 user and 1 role for each iteration).
If this activity is more regular, you might want to consider getting something developed. Maintaining 700 users to looks for a specific role to remove doesn't look like fun.
Regards
Colleen