Bug 15589: Changing 'his' to 'their' in OPAC lists

Bug 15589: Changing 'his' to 'their' in OPAC lists

To be more gender neutral

To test:
1) Go to OPAC lists (opac-shelves.pl)
2) Confirm it now says "Allow anyone to remove their own contributed
   entries."

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 229cc7e8be66b61b2a0070a83d63cb7afb513d3f)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
(cherry picked from commit d26086a84c9909dcc96d4f35086f4028a3e4c8bd)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>