Remove legacy support for shell 1.x

[jvalkeal]

It's time to drop legacy support for shell 1.x features like use of @CliAvailabilityIndicator and @CliCommand. This and adapter existing to give so upgrade path from 1.x. to 2.x and we don't want to bring this burden into 3.x code base as it essentially required having old 1.x jars in classpath.

[jvalkeal]

I think this is now done.