Fix mac build

Test: `m nothing` on mac
Change-Id: Ibc377134dbcc5d40263697ef1e79fc31b16e0d1d
diff --git a/ui/build/sandbox_darwin.go b/ui/build/sandbox_darwin.go
index 56791f7..7e75167 100644
--- a/ui/build/sandbox_darwin.go
+++ b/ui/build/sandbox_darwin.go
@@ -16,7 +16,6 @@
 
 import (
 	"os/exec"
-	"path/filepath"
 )
 
 type Sandbox string