Move Deferred class from ZeroMQ to util

src/util.h

@@ -662,5 +662,17 @@ inline std::vector<std::wstring_view> split(const wchar_t* s, const wchar_t* del
     return split(std::wstring_view(s), std::wstring_view(delim));
 }
 
+/**
+ * Helper class that runs a function at destruction.
+ */
+class Deferred {
+public:
+    Deferred(std::function<void()> deferred) : deferred(std::move(deferred)) {}
+    ~Deferred() { deferred(); }
+
+private:
+    std::function<void()> deferred;
+};
+
 } // namespace util
 } // namespace zeek