rtw89fw: remove module build dirs and firmware

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 on stable/14 to
avoid any confusion (it was never attached to the build).

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.

X-MFC after: rtw89 only
Sponsored by: The FreeBSD Foundation

(cherry picked from commit cf94672363d6638b7268c05b4628b62bbfc8dbe5)
(cherry picked from commit 7ff12dd25ada486c4d33e854977514b2db690e7f)