Cleanup the extra layer of "flavour" that came into the build framework
when flavours were introduced at a time when it was not planned.
Make linters some more happy. [1]
Remove the special license hack to install additional files.
If DISABLE_LICENSES is set we still installed files making builds fail [2].
One would hope to always install the lincese files but simply disable
any checking by the framework.
Introduce a new way using LICENSE_COMB=multi to install the default
license file, the extra WHENCE and any possible extra firmware license
files. Technically this is an abuse of the system too but at least it
should work and not break non default options.
Based on: D45369 by jrm [1]
Reported by: pi [2]
Sponsored by: The FreeBSD Foundation