Change Stage X presets to the individual plugins?

[hzoo]

Ref babel/babel#7770

Not sure how automatic this should be. People should decide what plugins to opt-in to anyway? Either way if we remove them we'll have a message on what to upgrade? I guess it's weird on the tooling side because the output would change over time (maybe needs to have a date, or to say it's current as of x).

[nicolo-ribaudo]

I think that it should just do what the last published version of the presets does.
And we can replace the presets with all the plugins and log a message which asks users to check if their config file is what they wanted.

[nicolo-ribaudo]

#69