LibCore: Move LibGUI/GNotifier to LibCore/CNotifier.

LibGUI/GNotifier.h

@@ -1,26 +0,0 @@
-#pragma once
-
-#include <AK/Function.h>
-
-class GNotifier {
-public:
-    enum Event {
-        None        = 0,
-        Read        = 1,
-        Write       = 2,
-        Exceptional = 4,
-    };
-    GNotifier(int fd, unsigned event_mask);
-    ~GNotifier();
-
-    Function<void(GNotifier&)> on_ready_to_read;
-    Function<void(GNotifier&)> on_ready_to_write;
-
-    int fd() const { return m_fd; }
-    unsigned event_mask() const { return m_event_mask; }
-    void set_event_mask(unsigned event_mask) { m_event_mask = event_mask; }
-
-private:
-    int m_fd { -1 };
-    unsigned m_event_mask { 0 };
-};