Bug 17447: Remove unused vars from batchRebuildItemsTables.pl

Bug 17447: Remove unused vars from batchRebuildItemsTables.pl

Variables $extkey not used, %opt not used.
Variables $tmptest[...] not used, calling _build_tag_directory useless.
The script now does not only print help if you specify -t.
Sub defnonull tidied.
Rearranged modules, removed Dumper.

Test plan:
[1] Run the script with -t flag. The script should not only print usage
    statement, but should do a dry run. (Test this on a small database,
    or pass an additional where clause.)

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>