Remove unneeded 'using' clauses

mcs/class/System.Web/System.Web.SessionState_2.0/SessionIDManager.cs

@@ -28,7 +28,6 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
 #if NET_2_0
-using System.Security.Cryptography;
 using System.Web;
 using System.Web.Configuration;
 using System.Web.Util;

mcs/class/System.Web/System.Web.SessionState_2.0/SessionStateModule.cs

@@ -36,7 +36,6 @@ using System.ComponentModel;
 using System.Web.Configuration;
 using System.Web.Caching;
 using System.Web.Util;
-using System.Security.Cryptography;
 using System.Security.Permissions;
 using System.Threading;
 using System.Configuration;