There are 3 copies of the platform-specific page list:
- 1 outdated, hard-coded copy in developing-with-qt.qdoc
- 2 (doubled-up) auto-generated copies in platform-notes.qdoc

There is only one link in the entire documentation to the latter. Thus,
this patch removes that page, moves the auto-generated list to
developing-with-qt.qdoc, and redirects the sole link.

Change-Id: If5bbdc9523ed961d4842c15214a1781e0eecf601
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>