j3dutils: remove a bunch of unneeded casts to Sample

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
j3dutils: stop suppressing the DoubleBeuffering flag in JCanvas3D

While this should be OK, we currently explicitly check for both antialiasing
and doublebuffering in the joglpipeline capabilities which means this will never
allow antialiasing to be enabled for JCanvas3D.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>