event/*: use `using` instead of `typedef`

src/event/MaskMonitor.hxx

@@ -34,7 +34,7 @@
 class MaskMonitor final {
 	InjectEvent event;
 
-	typedef BoundMethod<void(unsigned) noexcept> Callback;
+	using Callback = BoundMethod<void(unsigned) noexcept>;
 	const Callback callback;
 
 	std::atomic_uint pending_mask;

src/event/SignalMonitor.hxx

@@ -26,7 +26,7 @@ class EventLoop;
 
 #include "util/BindMethod.hxx"
 
-typedef BoundMethod<void() noexcept> SignalHandler;
+using SignalHandler = BoundMethod<void() noexcept>;
 
 /**
  * Initialise the signal monitor subsystem.

src/event/SocketEvent.hxx

@@ -75,7 +75,7 @@ public:
 	 */
 	static constexpr unsigned IMPLICIT_FLAGS = ERROR|HANGUP;
 
-	typedef std::make_signed<size_t>::type ssize_t;
+	using ssize_t = std::make_signed<size_t>::type;
 
 	SocketEvent(EventLoop &_loop, Callback _callback,
 		    SocketDescriptor _fd=SocketDescriptor::Undefined()) noexcept