security: remove erroneous comment about capabilities.o link ordering

Back when we had half ass LSM stacking we had to link capabilities.o
after bigger LSMs so that on initialization the bigger LSM would
register first and the capabilities module would be the one stacked as
the 'seconday'.  Somewhere around 6f0f0fd4 (back in 2008) we
finally removed the last of the kinda module stacking code but this
comment in the makefile still lives today.

Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>