forms: getMonth() and getYear() are deprecated in java.util.Date

Change-Id: I31664bbd8c1c3b02e8a7381226d4d558b37466a2
Reviewed-on: https://gerrit.libreoffice.org/11690
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>