Don't store Exception in a variable

Author: jvazquez-r7

lib/msf/java/rmi/client.rb

@@ -110,7 +110,7 @@ def recv_return(opts = {})
 
           begin
             return_data = Rex::Proto::Rmi::Model::ReturnData.decode(StringIO.new(data))
-          rescue ::RuntimeError => e
+          rescue ::RuntimeError
             return nil
           end