Let is_super_admin() return false when a role/caps view is selected

[JoryHogeveen]

When a role or capability view is selected the current user is still the same. So if any plugins only validate a is_super_admin() check instead of current_user_can() these checks would return true.

Not 100% sure but I'd say that when a view is selected, is_super_admin() should return false.

• Maybe make it optional??
• Only disable on non-network admin pages

Tests:
This effectively disables functions grant_super_admin() and revoke_super_admin() since it sets/changes the $super_admins global variable. So when you switch to another super admin (as a superior admin) adding other users to the super admin list should not work.