Bug 16830: Remove -x usage on koha-indexer

Bug 16830: Remove -x usage on koha-indexer

This patch just does that, and removes it from the comment on /etc/default/koha-common

To test:
- Apply the patch
- Run:
  $ vagrant ssh ; cd kohaclone
  $ sudo debian/scripts/koha-indexer --stop kohadev
  $ sudo debian/scripts/koha-indexer --start kohadev
=> SUCCESS: Verify no warning is shown on the indexer-output.log file
- Sign off

https://bugs.koha-community.org/show_bug.cgi?id=16830

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>