Fix typo in deletelangdialog.ui

Change-Id: I20602fb7f048c2c79073b47539cad6419fb90bb5
Reviewed-on: https://gerrit.libreoffice.org/12969
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>