Update APIs to use new Google cloud paths.

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

 // AUTOGENERATED. DO NOT EDIT.
 
 package helloworld
 
 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{
                         "helloworld.Greeter",
                 },
                 []byte{31, 139,
                         8, 0, 0, 9, 110, 136, 0, 255, 108, 147, 65, 79, 219, 64,
                         16, 133, 189, 142, 19, 146, 33, 52, 100, 11, 36, 181, 42, 117,
                         154, 3, 160, 10, 28, 72, 139, 122, 171, 132, 16, 42, 84, 148,
@@ skipping 47 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("helloworld.Greeter")
         if err != nil {
                 panic(err)
         }
         return ret
 }