Do not recommend deprecated subcommands

[donovanglover]

Hello,

As a new user to Yarn, I was confused when yarn licenses told me to use yarn licenses ls, and then after using yarn licenses ls I was told to use yarn licenses list instead.

I propose that all deprecated methods are not recommended as possible subcommands. If there are other areas like this, please tell me, as I don't think any deprecated methods should be recommended.

If you don't mind, I'd like to work on this issue. I went through the code base and it seems like a fairly trivial fix (add a deprecated flag and only join subcommands that aren't deprecated).