Remove qtdemo from gitignore

QtDemo was removed with a commit in qtdoc.

Change-Id: I1803e041e7da57641148a37691ffdc6ae6c85ad9
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>

.gitignore

@@ -81,7 +81,6 @@ bin/pixeltool*
 bin/qmake*
 bin/qdoc*
 bin/qt3to4*
-bin/qtdemo*
 bin/qttracereplay*
 bin/rcc*
 bin/uic*