Do not mention deleting old versions of Paperback

[PythonCoderAS]

The Testflight guides both mention deleting any other installed version of Paperback before installing the new one. However, this is not always necessary, especially if a Public Testflight user is upgrading to a Patreon Testflight account. I think mentioning that Public Testflight users can normally upgrade to the Patreon version would help.