Remove builtin features

[alexdima]

Stop shipping features defined in vscode-dev-containers and switch to rely entirely on feature resolving as defined via devcontainers/spec#7

Blocked by:

• Distributing features & templates spec#7
• Avoid dropping existing features features#64

[samruddhikhandale]

Working on CLI changes to automatically map the old feature names to their new locations for back compatibility.
Also, mapping deprecated features from here to microsoft/vscode-dev-containers

(I'll only create a PR and keep it ready for 🚀 )

[samruddhikhandale]

PR -

• Auto mapping feature ids from old shorthand syntax to devcontainers/features #100

Waiting for

• Initial version of OCI packages for features. #94