Having to include some dummy class is suboptimal and we no longer need to
do this. Also move this check to populate_sdk_base since we then don't
need to include it in toolchains specifically.
(From OE-Core rev: 2ee979ff71d31e497be856ea1443667c6d799d34)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>