common-licences: remove ambiguous "BSD" license

Our "BSD" license is the 3-clause BSD license, but many recipes were
using "BSD" for any variation of the license.

We've mostly moved recipes away from the vague "BSD" license to concrete
names such as "BSD-3-Clause", so delete the BSD license to force the
remaining users to update their license statements.

[ YOCTO #14539 ]

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>