Bug 11245: fix typo in modborrowers.tt javascript string

Bug 11245: fix typo in modborrowers.tt javascript string

In modborrowers.tt, Bug 8986 made the javascript strings translatable:
  _("This attribute will be only applied to the patron\'s category")

In this case, the backslash is useless.

Test plan :
- Create a borrower attribute with a "Category" defined
- Go to Tools / Batch patrons modification
- Enter a cardnumber and submit
- Next to "Attribute", select the borrower attribute you created
=> You see a grey text at the right : This attribute will be only
   applied to the patron's category "XXX"

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>