[FEATURE] Remove deprecated Persistent Cache methods

[johnboxall]

Approximately one million web years, Managed Runtime supported a feature called "Persistent Cache".

This feature was deprecated and removed from Managed Runtime – however, some of the public method stubs for interacting with it remain in the PWA Kit code:

Most of the code is here:

https://github.com/SalesforceCommerceCloud/pwa-kit/blob/c65d9a8b28268b6f9b1d87462cf47c4c31fb5476/packages/pwa-kit-runtime/src/ssr/server/express.js#L28-L387 https://github.com/SalesforceCommerceCloud/pwa-kit/blob/develop/packages/pwa-kit-runtime/src/utils/ssr-cache.js

But it is likely that there might be more code.

Removing it would simplify the codebase and prevent folks from being confused by methods that don't do anything.

Previously, we replaced some of the public API surface here with stubs: https://github.com/SalesforceCommerceCloud/pwa-kit/pull/949

[git2gus[bot]]

This issue has been linked to a new work item: W-14508736