LibGUI: Remove unused method definitions from GlyphMapWidget

These got added recently but were never implemented, so let's remove
them. :^)

Userland/Libraries/LibGUI/GlyphMapWidget.h

@@ -71,10 +71,6 @@ private:
 
     Gfx::IntRect get_outer_rect(int glyph) const;
 
-    void cut_glyph(int glyph);
-    void copy_glyph(int glyph);
-    void paste_glyph(int glyph);
-    void delete_glyph(int glyph);
     void recalculate_content_size();
 
     int m_glyph_count { 0x110000 };