remove very old upgrade instructions

Author: beaugunderson

README.md

@@ -14,20 +14,6 @@
 `ip-address` is a library for validating and manipulating IPv4 and IPv6
 addresses in JavaScript.
 
-
-### Migrating from 6.x to 7.x
-
-`ip-address` was rewritten in TypeScript for version 7. If you were using
-version 6 you'll need to make these changes to upgrade:
-
-- Instead of checking `isValid()`, which has been removed, you'll need to use a
-  `try`/`catch` if you're accepting unknown input. This made the TypeScript
-  types substantially easier as well as allowed the use of an `AddressError`
-  class which will contain a `parseMessage` if an error occurred in the parsing
-  step.
-- Instead of using the `error`, `parseError`, and `valid` attributes you'll
-  need to use the `message` and `parseMessage` of the thrown `AddressError`.
-
 ### Documentation
 
 Documentation is available at [ip-address.js.org](http://ip-address.js.org/).