javaunohelper: Using "final" modifier whenever applicable in java

All classes that belongs to the com.sun.star.lib.uno.adapter package are not part of the stable URE interface.
(cf. <http://api.libreoffice.org/docs/java/ref/index.html>), for that reason those classes may be final.

Remove unused import in com.sun.star.comp.helper.ComponentContext class.

Change-Id: I68be8da4324f5163505e65365bf49a6a9cd00672
Signed-off-by: Stephan Bergmann <sbergman@redhat.com>