tidy up code

Author: firefart

lib/rex/post/meterpreter/ui/console/command_dispatcher/mimikatz.rb

@@ -159,7 +159,7 @@ def get_privs
   end
 
   def system_check
-    unless (client.sys.config.is_system?)
+    unless client.sys.config.is_system?
       print_warning("Not currently running as SYSTEM")
       return false
     end