* plugin/dnstap: remove config struct

this struct is an uneeded intermidiate to get a dnstap it can be
removed. Remove the dnstapio subpkg: it's also not needed. Make *many*
functions and structs private now that we can.
Signed-off-by: Miek Gieben <miek@miek.nl>

* correct logging
Signed-off-by: Miek Gieben <miek@miek.nl>