iwlwifi: mvm: remove netdetect debugfs entry

This debugfs entry was implemented just as a proof-of-concept before
the full support for netdetect via cfg80211/mac80211 was implemented.
Now that we have a proper way to enable netdetect from userspace, this
entry is redundant and should be removed to avoid unnecessary
maintenance work.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>