Remove old SwapSelection package from channels.json

As suggested by @FichteFoll:

@ both, if gillibrand's package provides the same functionality as
chenha0 but also works for ST3, it is superior to it. It only has 37
installs according to the stats, but imo you should replace the package
with your version because it is still being maintained. In order to to
that, you should remove his entry in channel.json and then you can
either let your package have the same name or add a previous_names key
that includes the old one.