The current code didn't run the tests anymore, but was still
based on the assumption that qtbase/configure set up the
right configuration.

Clean up the pro files for mng and tiff while we're at it.

Change-Id: Iee46c183fda57ec07b60a80089af7925db959c40
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>