See http://thread.gmane.org/gmane.games.flightgear.devel/77094/focus=77496 and
the surrounding thread for discussions.
This removes the following: the old opus.mdl Microsoft Flight Simulator file,
probably for this aircraft https://en.wikipedia.org/wiki/ARV_Super2, which only
the Marchetti S.211 UIUC FDM aircraft pointed to but never used; the
sopwithCamel-v2-nl aircraft which was never developed past copying the
sopwithCamel-v1-n1 UIUC FDM data table files; and the README.uiuc.html file
which is redundant as equivalent text is found in all UIUC aircraft directories.
