SW: drop dstat (unmaintained upstream)

SW: drop dstat (unmaintained upstream)

dstat got removed from Debian/testing due to autopkgtest failures,
and quoting from https://bugs.debian.org/1034856:

| The reality of the situation is that dstat is fairly buggy. Still usable
| in many cases, but far from perfect. Unfortunately the project is not
| maintained upstream since several years [1], and fixing the outstanding
| issues is not trivial. All my hopes are now on dool, which seems to be a
| promising replacement and is currently being packaged [2].
|
| [1] https://github.com/dstat-real/dstat/issues/170
| [2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1032875