jogl: remove clone() version that can only ever fail

commit:
d75835796900cac602f7e5789601ffba0a27efe2 (Graph: More std. functionality (equals, clone) / Better in-place transformation (cubic -> quadratic))

Added a clone method, but did not implement Cloneable, meaning Object.clone() will
always throw CloneNotSupportedException.  This method never returns anythng but null.

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