[glibmm] example: Remove unnecessary virtual keywords on destructors.

[Murray Cumming <murrayc src gnome org>]

commit 633cb807b6f42575f4fd409a61ea32085f9edf39
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Dec 24 12:13:18 2015 +0100

    example: Remove unnecessary virtual keywords on destructors.

 examples/markup/parser.cc     |    2 +-
 examples/thread/dispatcher.cc |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/examples/markup/parser.cc b/examples/markup/parser.cc
index b954a67..ef45dac 100644
--- a/examples/markup/parser.cc
+++ b/examples/markup/parser.cc
@@ -51,7 +51,7 @@ class DumpParser : public Glib::Markup::Parser
 {
 public:
   DumpParser();
-  virtual ~DumpParser();
+  ~DumpParser() override;
 
 protected:
   void on_start_element(Glib::Markup::ParseContext& context,
diff --git a/examples/thread/dispatcher.cc b/examples/thread/dispatcher.cc
index 85643b0..50e3b53 100644
--- a/examples/thread/dispatcher.cc
+++ b/examples/thread/dispatcher.cc
@@ -31,7 +31,7 @@ class ThreadProgress
 {
 public:
   explicit ThreadProgress(int the_id);
-  virtual ~ThreadProgress();
+  ~ThreadProgress();
 
   int  id() const;
   void launch();
@@ -60,7 +60,7 @@ class Application : public sigc::trackable
 {
 public:
   Application();
-  virtual ~Application();
+  ~Application();
 
   void run();