buildroot

xenomai: restrict installed files further

Xenomai 3 installs quite some utils and other programs to the target
filesystem, many of which will not be used by most users.

As it is currently unclear which utils are effectively useful, and as it is
undesirable to create config options for each individual util, remove all
remaining utils such that only the Xenomai libraries remain.

At the point it becomes clear that certain utils _are_ desired by some
users, we can identify how to group them in relevant config options.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>