These interfaces were added in aacddda89d, with
no clear motivation, other than "Also hide ViewDB behind an interface".
This patch removes the interface in favor of using a concrete implementation;
There's currently only one implementation of this interface, and if we would
decide to change to an alternative implementation, we could define relevant
interfaces on the receiver side.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>