HexEditor: Remove unused readonly flag

`HexEditor::set_readonly` was never called, even though
`HexEditor::is_readonly` was occasionally queried -- so it's entirely
been removed.

Userland/Applications/HexEditor/HexEditor.cpp

@@ -49,13 +49,6 @@ HexEditor::HexEditor()
     m_blink_timer->start();
 }
 
-void HexEditor::set_readonly(bool readonly)
-{
-    if (m_readonly == readonly)
-        return;
-    m_readonly = readonly;
-}
-
 bool HexEditor::open_new_file(size_t size)
 {
     auto maybe_buffer = ByteBuffer::create_zeroed(size);
@@ -460,7 +453,7 @@ void HexEditor::keydown_event(GUI::KeyEvent& event)
         return;
     }
 
-    if (!is_readonly() && !event.ctrl() && !event.alt() && !event.text().is_empty()) {
+    if (!event.ctrl() && !event.alt() && !event.text().is_empty()) {
         if (m_edit_mode == EditMode::Hex) {
             hex_mode_keydown_event(event);
         } else {

Userland/Applications/HexEditor/HexEditor.h

@@ -32,9 +32,6 @@ public:
 
     virtual ~HexEditor() override = default;
 
-    bool is_readonly() const { return m_readonly; }
-    void set_readonly(bool);
-
     size_t buffer_size() const { return m_document->size(); }
     bool open_new_file(size_t size);
     void open_file(NonnullRefPtr<Core::File> file);
@@ -74,7 +71,6 @@ protected:
     virtual void keydown_event(GUI::KeyEvent&) override;
 
 private:
-    bool m_readonly { false };
     size_t m_line_spacing { 4 };
     size_t m_content_length { 0 };
     size_t m_bytes_per_row { 16 };