LibCore: Don't double-check select() in Socket's read notifier callback

This was used to work around a possible bug where select() would mark a
socket readable, but another user of the same socket would read before
the notifier's callback is run; let's remove this and fix any issues
regarding that specific situation later when they pop up.

Userland/Libraries/LibCore/Socket.cpp

@@ -213,8 +213,6 @@ void Socket::ensure_read_notifier()
     VERIFY(m_connected);
     m_read_notifier = Notifier::construct(fd(), Notifier::Event::Read, this);
     m_read_notifier->on_ready_to_read = [this] {
-        if (!can_read())
-            return;
         if (on_ready_to_read)
             on_ready_to_read();
     };