Docs: Remove partner documentation in favor of new repo (#11302)

Now that we are providing functionality for hosting partners to provision WooCommerce extensions as well as Jetpack plans, it makes sense to put the documentation in a single location.

This PR removes the Jetpack hosting partner documentation from the Jetpack repo in favor of the documentation that now lives at:

https://github.com/Automattic/host-partner-documentation

#### Changes proposed in this Pull Request:
<!--- Explain what functional changes your PR includes -->

* Remove hosting partner documentation and link to new documentation location.

#### Testing instructions:
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* Ensure that link to new documentation location works.

#### Proposed changelog entry for your changes:
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* Removes hosting partner documentation in favor of new documentation repository.

docs/partners/README.md

@@ -1,24 +1,5 @@
 # Welcome to the Jetpack Hosting Partners Program!
 
-To make documentation easier for our partners to view, and to ensure our partners are always viewing the most up-to-date documentation, we've decided to source-control the documentation in the Jetpack directory itself.
+Documentation for the hosting partners program has moved to a new repository. Please visit the following link for documentation and contact information:
 
-In this directory, you'll find information such as how to provision and cancel Jetpack plans as well as how to customize Jetpack.
-
-If you have any technical questions or concerns, don’t hesitate to get in touch with Eric Binnion (@ebinnion) at [email protected].
-
-## Documentation links
-
-- Plan provisioning
-  - [Via CLI](plan-provisioning.md)
-  - [Via direct API call](plan-provisioning-direct-api.md)
-  - [Automatic account creation](automatic-account-creation-connection.md)
-  - [Controlling the redirect after a user finishes connection authorization](redirect-after-authorization.md)
-- Checking status
-  - [Connection status](determining-connection-status.md)
-  - [Provisioning status](determining-provisioning-status.md)
-- [Managing modules](managing-modules.md)
-- [Upgrade redirection](upgrade-redirection.md)
-
-## Become a Jetpack Hosting Partner
-
-If you're not already a Jetpack Hosting Partner and you'd like some more information, head on over to [https://jetpack.com/for/hosts/](https://jetpack.com/for/hosts/) to get started!
+[https://github.com/Automattic/host-partner-documentation](https://github.com/Automattic/host-partner-documentation)