Revert "Add --io as a valid option" not needed I guess?

This reverts commit 17766c4.

Author: scottchiefbaker

dool

@@ -201,7 +201,7 @@ class Options:
                 self.netlist = arg.split(',')
             elif opt in ['-p']:
                 self.plugins.append('proc')
-            elif opt in ['-r', '--io']:
+            elif opt in ['-r']:
                 self.plugins.append('io')
             elif opt in ['-s']:
                 self.plugins.append('swap')