[task scheduler] Move files from build_scheduler/ to task_scheduler/

task_scheduler/go/db/db.go

 package db
 
 import (
         "errors"
         "io"
         "time"
 
         "github.com/skia-dev/glog"
 )
 
@@ skipping 139 matching lines @@
         } else {
                 return tasks[0], nil
         }
 }
 
 // RemoteDB allows retrieving tasks and full access to comments.
 type RemoteDB interface {
         TaskReader
         CommentDB
 }