Changed qpixmap unittest to remove created file after run.

- Removes temp_image.png after test run.

Change-Id: I0b233609c2bbf57151cf173181a40738d934f0ec
Reviewed-by: Kurt Korbatits  <kurt.korbatits@nokia.com>
Reviewed-by: Jason McDonald <jason.mcdonald@nokia.com>
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>

tests/auto/gui/image/qpixmap/tst_qpixmap.cpp

@@ -79,6 +79,7 @@ public:
 public slots:
     void init();
     void cleanup();
+    void cleanupTestCase();
 
 private slots:
     void swap();
@@ -215,6 +216,11 @@ void tst_QPixmap::cleanup()
 {
 }
 
+void tst_QPixmap::cleanupTestCase()
+{
+    QFile::remove(QLatin1String("temp_image.png"));
+}
+
 void tst_QPixmap::swap()
 {
     QPixmap p1( 16, 16 ), p2( 32, 32 );