Remove duplicate properties

There are properly-cased TrakEM2 and Skeletonize3D properities, let's
remove the improperly-cased ones.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Remove three unmaintained projects

They were already removed from the current development version of the
sc.fiji:fiji project...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>