src/poky:kernel.bbclass: remove unused CMDLINE_CONSOLE

CMDLINE_CONSOLE appears to be a legacy variable that is unused anywhere,
and has not been modified the creation of the git tree.  Remove it and
make life simpler.

(From OE-Core rev: d075b7c8f15488d98f0cda7b59de9dbed2a4f2d1)

Signed-off-by: Jon Mason <jdmasonkudzu.us>
Signed-off-by: Alexandre Belloni <alexandre.bellonibootlin.com>
Signed-off-by: Richard Purdie <richard.purdielinuxfoundation.org>

Author: jonmason