rtw8xfw: remove module build dirs for firmware long gone
rtw88 and rtw89 firmware files were removed from main a year ago
after core members asked to not import more biinary blobs into main.
Also remove the module build framework for them being long gone.
People are asked to use fwget(8) to automatically install firmware
from ports according to the man page. A solution for the install
media is still pending.
Fixes: cf94672363d6638b7268c05b4628b62bbfc8dbe5
MFC after: 3 days (rtw89 only)
Sponsored by: The FreeBSD Foundation