Stop registering servers from cache if the servers are not in the list of servers returned by the provider

[DonJayamanne]

• We have 3 servers from provider
• These 3 are saved in cache
• Reload VS Code
• The 3 servers are loaded from cache and we end up registering kernel finders for them.
• However provider returns 0 servers

For extensions adopting the new API, we should stop loading the old servers from cache and remove them completely. Until they are added, this means we will need to track the whether an extension is using the new API or not.

For AzML, GitHub and internal extension we can leave the old behaviour For all other extensions assume they will end up using the new API (or some similar safe approach).

[DonJayamanne]

This has already been done.