Use sh_binary for a host shell script.

It's more apt than cc_prebuilt_binary, and the latter breaks when it
starts to symlink to the source tree, because the script looks for
shflags relative to `readlink -f $0`.

Test: m dist
Bug: 145934348
Change-Id: I8bc80a43046e4553aa399e2ab77d268e11be325b
diff --git a/Android.bp b/Android.bp
index f61b255..a8b5fc2 100644
--- a/Android.bp
+++ b/Android.bp
@@ -730,12 +730,12 @@
 
 // Brillo update payload generation script
 // ========================================================
-cc_prebuilt_binary {
+sh_binary {
     name: "brillo_update_payload",
     device_supported: false,
     host_supported: true,
 
-    srcs: ["scripts/brillo_update_payload"],
+    src: "scripts/brillo_update_payload",
     required: [
         "delta_generator",
         "shflags",