Update APIs to use new Google cloud paths.

grpc/prpc/talk/buildbot/proto/pb.discovery.go

 // AUTOGENERATED. DO NOT EDIT.
 
 package buildbot
 
 import discovery "github.com/luci/luci-go/grpc/discovery"
 
-import "github.com/luci/luci-go/common/proto/google/descriptor"
+import "google.golang.org/genproto/protobuf"
 
 func init() {
         discovery.RegisterDescriptorSetCompressed(
                 []string{
                         "buildbot.Buildbot",
                 },
                 []byte{31, 139,
                         8, 0, 0, 9, 110, 136, 0, 255, 148, 87, 203, 114, 219, 200,
                         21, 37, 128, 6, 13, 53, 197, 135, 32, 241, 33, 136, 182, 219,
                         180, 108, 61, 44, 83, 99, 169, 52, 138, 102, 60, 21, 89, 180,
@@ skipping 131 matching lines @@
 //
 // Do NOT modify the returned descriptor.
 func FileDescriptorSet() *descriptor.FileDescriptorSet {
         // We just need ONE of the service names to look up the FileDescriptorSet.
         ret, err := discovery.GetDescriptorSet("buildbot.Buildbot")
         if err != nil {
                 panic(err)
         }
         return ret
 }