I left the way as „removed:highway“, because it is still visible in the latest aerial image and to prevent it to be remapped. 
It looks like the way has been removed recently.
I found a offical announcement of Gemeente Sluis from 2015 where the removal of this fietspad was announced. Reasons were the bad state of the surface and enough alternative routes for bicycles.
(https://zoek.officielebekendmakingen.nl/stcrt-2015-27872.pdf)