LibCore+LibTLS: Don't keep a "ready to write" notifier on all Sockets

The "ready to write" notifier we set up in generic socket connection is
really only meant to detect a successful connection. Once we have a TCP
connection, for example, it will fire on every event loop iteration.

This was causing IRC Client to max out the CPU by getting this no-op
notifier callback over and over.

Since this was only used by TLSv12, I changed that code to create its
own notifier instead. It might be possible to improve TLS performance
by only processing writes when actually needed, but I didn't look very
closely at that for this patch. :^)

Libraries/LibCore/Socket.h

@@ -63,7 +63,6 @@ public:
 
     Function<void()> on_connected;
     Function<void()> on_ready_to_read;
-    Function<void()> on_ready_to_write;
 
 protected:
     Socket(Type, Object* parent);