Welcome to OSM. If these trails are private, deleting them is not the correct solution - someone will just add them back anyways (because they assume that they are missing). Instead, we can add additional access tags which indicate that the trails are private access. I will probably do this in the next few days.

See also:
https://wiki.openstreetmap.org/wiki/Why_we_won%27t_delete_roads_on_private_property

Let me know if you have any questions !