Remove references to QT_INSTALL_DEMOS & DemosPath.

Remove references to QT_INSTALL_DEMOS & DemosPath.

The distinction between 'examples' and 'demos' is completely blurred at
this point. We've decided, with the SDK people, to scrap the existing
terminology in favor of the word 'example' only -- distinguishing
between code snippets, walkthroughs, "demonstrations" can be done
via keywords or some other method.

Removing QT_INSTALL_DEMOS from all .pro files in Qt is still in
progress.

Change-Id: I86fc0e40d54baa54c5641fc6acbd8b67e4ad2789
Reviewed-on: http://codereview.qt.nokia.com/1034
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Marius Storm-Olsen <marius.storm-olsen@nokia.com>