overlay: Add missing make-flashable-zip.

This was broken in a hastily done rebase :/

overlay/mobile-nixos/android-flashable-zip/make-flashable-zip.nix

@@ -0,0 +1,29 @@
+{ runCommandNoCC, writeText, zip, mobile-nixos }:
+
+let
+  inherit (mobile-nixos) android-flashable-zip-binaries;
+in
+
+{ script, copyFiles, name }:
+
+let
+  update-script = writeText "update-script.rb" script;
+in
+runCommandNoCC name {
+  nativeBuildInputs = [
+    zip
+  ];
+} ''
+  mkdir -p zip
+  (
+    echo ":: Archiving flashable zip"
+    PS4=" $ "
+    set -x
+    cd zip
+    mkdir -p META-INF/com/google/android
+    ${copyFiles}
+    cp ${update-script} update-script.rb
+    cp ${android-flashable-zip-binaries}/bin/update-binary META-INF/com/google/android/update-binary
+    zip $out $(find | sort)
+  )
+''