cmd/coordinator: switch to UBA on snapshots and logs

I'm enabling UBA on go-build-log and go-build-snapshots, at which point
setting per-object ACLs will fail.

For golang/go#53890.

Change-Id: I9fe0d423146daedcc71b88ba03d035404279bb58
Reviewed-on: https://go-review.googlesource.com/c/build/+/418793
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

cmd/coordinator/buildstatus.go

@@ -25,7 +25,6 @@ import (
 	"time"
 
 	"cloud.google.com/go/errorreporting"
-	"cloud.google.com/go/storage"
 	"go4.org/syncutil"
 	"golang.org/x/build/buildenv"
 	"golang.org/x/build/buildlet"
@@ -894,7 +893,6 @@ func (st *buildStatus) writeSnapshot(bc buildlet.Client) (err error) {
 	}
 	wr := sc.Bucket(bucket).Object(st.SnapshotObjectName()).NewWriter(ctx)
 	wr.ContentType = "application/octet-stream"
-	wr.ACL = append(wr.ACL, storage.ACLRule{Entity: storage.AllUsers, Role: storage.RoleReader})
 	if n, err := io.Copy(wr, tgz); err != nil {
 		st.logf("failed to write snapshot to GCS after copying %d bytes: %v", n, err)
 		return err

cmd/coordinator/coordinator.go

@@ -2025,10 +2025,6 @@ func newBuildLogBlob(objName string) (obj io.WriteCloser, url_ string) {
 
 	wr := pool.NewGCEConfiguration().StorageClient().Bucket(bucket).Object(objName).NewWriter(context.Background())
 	wr.ContentType = "text/plain; charset=utf-8"
-	wr.ACL = append(wr.ACL, storage.ACLRule{
-		Entity: storage.AllUsers,
-		Role:   storage.RoleReader,
-	})
 
 	return wr, fmt.Sprintf("https://storage.googleapis.com/%s/%s", bucket, objName)
 }