New :remove command

[nik-rev]

It's useful to be able to delete the current file. When #11164 is merged you'll be able to do it with :sh rm %{f}.

But when you do that, the current file is still loaded. If you use :reload you'll get an error Can't find file to reload from "file.txt"

What would be nice alternative, is when you run :remove, you are force switched to a different open buffer. If none are open, a scratch buffer is open instead.

[the-mikedavis]

Duplicate of #4592