Nations: Adds deletion of subfield in each re-run

* Changes the check_nations.py plugin to delete the 'w' subfield
  in the fields '100' and '700' everytime the plugin runs

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
Merge branch 'nations' of https://github.com/mvesper/scoap3 into mvesper-nations
Merge branch 'mvesper-nations'