LibGUI: Remove reference captures of stack variables in ProcessChooser

Since all reference-captured variables where pointers to non-stack
objects whose owners outlive the lambdas, things were fine in practice,
but it's a bit brittle and it makes a change I want to make in this code
more difficult.

Libraries/LibGUI/ProcessChooser.h

@@ -47,6 +47,7 @@ private:
     String m_window_title;
     String m_button_label;
     RefPtr<Gfx::Bitmap> m_window_icon;
+    RefPtr<TableView> m_table_view;
 
     bool m_refresh_enabled { true };
     unsigned m_refresh_interval { 1000 };