db: Remove column_family stub
db: Remove column_family stub

There's a proper column_family in database.hh now. Remove a stub that
was introduced during the initial conversion.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@cloudius-systems.com>

justintung/scylla,raphaelsc/scylla,eklitzke/scylla,stamhe/scylla,rentongzhang/scylla,phonkee/scylla,respu/scylla,phonkee/scylla,rentongzhang/scylla,tempbottle/scylla,capturePointer/scylla,aruanruan/scylla,raphaelsc/scylla,rluta/scylla,stamhe/scylla,dwdm/scylla,gwicke/scylla,phonkee/scylla,stamhe/scylla,acbellini/scylla,eklitzke/scylla,guiquanz/scylla,kangkot/scylla,tempbottle/scylla,dwdm/scylla,respu/scylla,scylladb/scylla,kangkot/scylla,bowlofstew/scylla,scylladb/scylla,rluta/scylla,rluta/scylla,duarten/scylla,justintung/scylla,kangkot/scylla,gwicke/scylla,glommer/scylla,eklitzke/scylla,scylladb/scylla,avikivity/scylla,shaunstanislaus/scylla,justintung/scylla,victorbriz/scylla,senseb/scylla,glommer/scylla,duarten/scylla,capturePointer/scylla,shaunstanislaus/scylla,kjniemi/scylla,linearregression/scylla,aruanruan/scylla,duarten/scylla,asias/scylla,bowlofstew/scylla,capturePointer/scylla,acbellini/scylla,senseb/scylla,guiquanz/scylla,respu/scylla,avikivity/scylla,acbellini/scylla,shaunstanislaus/scylla,kjniemi/scylla,asias/scylla,tempbottle/scylla,scylladb/scylla,asias/scylla,glommer/scylla,bowlofstew/scylla,rentongzhang/scylla,senseb/scylla,gwicke/scylla,avikivity/scylla,kjniemi/scylla,wildinto/scylla,wildinto/scylla,linearregression/scylla,victorbriz/scylla,guiquanz/scylla,dwdm/scylla,linearregression/scylla,aruanruan/scylla,raphaelsc/scylla,victorbriz/scylla,wildinto/scylla