Removing Membership Status Message on Front End Webform
I suggest you disable the membership types you are no longer using in your system (per Pete's suggestion in the comments).

I've just patched webform_civicrm to ensure it takes this into account, so it will no longer display messages about disabled membership types. That will be included in the 7.x-4.16 release, for now you can upgrade to the -dev version of the module to get this new functionality.