[INTERNAL] Address warnings and prune dead code

This removed unused variables, fields, and method parameters -- some of
which were presented as warnings, others were found by FindBugs.
Furthermore, this patch removes unnecessary String.toString() calls and
sets false {@link ...} annotations straight.

Change-Id: Ic69a0855603b766d9d4d299110adeca546ccee1f
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1496
Tested-by: Jenkins CI
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>