license/insane: Show warning for obsolete license usage

We want to use SPDX identifiers in LICENSE variables. There is now a
conversion script to make most of the translations. Add a list of
strings which have been replaced so we can show warnings to users
if they're still used anywhere.

Add checks to the package as insane check. This is currently a warning
by default but can be turned off or made an error as per the other standard
checks.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>