kernel-yocto: remove unnecessary non-bare warning

kernel-yocto: remove unnecessary non-bare warning

In the past working from a non-bare clone would cause problems,
due to branches not existing in the WORKDIR clone. This hasn't
been true for some time, since the routines which convert remotes
into local branches have been functioning without problems.

So we no longer need the warning and it can be removed.

(From OE-Core rev: 42d42c24a37af0ea8896087c7cc8215eb19f633d)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>