[dnsdist] dnsdist package from master repo

[Christoph]

> The dnsdist version in the buster master repo looks a bit odd
> "0.0.16738+0.g867916f6a1-1pdns.buster" and is lower than the one in
> debian (1.3.3-3) which doesn't make it an install candidate unless we
> change the pinning.

that was not correct (it is an install candidate)