scripts: Add `delete-remote-branches` script

This is useful for cleaning up remote branches that are no longer used.

scripts/delete-remote-branches.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+# Delete all remote branches that don't have a local copy.
+
+remote="rad"
+
+# Iterate over all remote branches.
+for branch in $(git branch -r --format "%(refname:short)"); do
+  # Extract the branch name without the "$remote/" prefix.
+  branch=${branch#"$remote/"}
+  # Never delete the master branch.
+  if [ "$branch" == "master" ]; then
+    continue
+  fi
+
+  # Check if the branch doesn't exist locally.
+  if ! git rev-parse --quiet --verify "$branch" >/dev/null; then
+    git push -o "no-sync" $remote --delete "$branch"
+    echo "Deleted '$branch'"
+  fi
+done
+
+rad sync --announce