[milo] remove linkBase and calculate links directly.

milo/buildsource/buildbucket/pubsub.go

Index: milo/buildsource/buildbucket/pubsub.go
diff --git a/milo/buildsource/buildbucket/pubsub.go b/milo/buildsource/buildbucket/pubsub.go
index a80bbfea35f68f57350fb3c55fae1f11bbadecf7..1aea2c4af97c89fb0958be0293c1ff8c85c2dc81 100644
--- a/milo/buildsource/buildbucket/pubsub.go
+++ b/milo/buildsource/buildbucket/pubsub.go
@@ -99,8 +99,7 @@ func maybeGetBuild(
 		return nil, err
 	}
 	bl := swarming.BuildLoader{}
-	// The linkBase is not necessary for the summary.
-	return bl.SwarmingBuildImpl(c, swarmingSvc, "", task)
+	return bl.SwarmingBuildImpl(c, swarmingSvc, task)
 }
 
 // processBuild queries swarming and logdog for annotation data, then adds or