remove obsolete strings

src/main/res/values/strings.xml

@@ -645,9 +645,6 @@
     <string name="actionbar_contacts">Back up contacts</string>
     <string name="actionbar_contacts_restore">Restore contacts</string>
     <string name="contacts_backup_button">Back up now</string>
-    <string name="contacts_restore_button">Restore last backup</string>
-    <string name="contacts_header_restore">Restore</string>
-    <string name="contacts_header_backup">Backup</string>
     <string name="contacts_automatic_backup">Automatic backup</string>
     <string name="contacts_last_backup">Last backup</string>
     <string name="contacts_read_permission">Permission to read contact list needed</string>