refs https://github.com/TryGhost/Toolbox/issues/354
- these READMEs were migrated over from when each package was in a
different repo
- they also assume you're going to be publishing the packages because it
mentions install instructions
- only a few of them contain custom content
- this commit deletes the majority of these files because they're now
not useful
- any that contained other instructions have been cut down
