Release Notes: Hardware Compat: remove rtwn_usb from Ethernet drivers

The previous commit (60f8423a1ce27) correctly adds rtwn_usb in the
wireless network section.
There is another reference to rtwn_usb in the Ethernet section which is
wrong there. Remove it.

Reviewed by: bz
Differential Revision: https://reviews.freebsd.org/D47507