remove the bogus annotations section

[vbatts]

trigger -> https://github.com/opencontainers/image-spec/pull/809/files#r667082904

discoveries:

• conversion: add platform conversions #711
• conversion: add document about image -> runtime configuration #492
• https://github.com/opencontainers/umoci/blob/07fa845e5b068dee64dcbf391b456a564a6fcfa6/oci/config/convert/runtime.go#L32-L42

I think this section of conversion of Config.labels to some annotations is not actually use in the wild.
Lets just remove it