fix ropes compat code

[Buckaroo Banzai]

Seems to crash on the destroy part of the ropes with an unknown content_id:
pandorabox-io/pandorabox.io#489

[tuedel]

This should be fixed now since minetest-mods/ropes#20 has been merged.

[Buckaroo Banzai]

thanks @tuedel, i also reverted the rope-disabling commit