Remove solvedb API and other related stuff

Remove solvedb API and other related stuff
- nobody has used the solvedb for anything in years
- the mechanism + rpmcache are horribly broken on multilib
- solvedb is way too heavyweight to be really usable as a general mechanism
- solver callback hook left in place as that could in theory be usable still
- we need something better to replace this all, getting rid of it now
  so we're not stuck with the API forever