Kernel: drop bluetooth support

Kernel: drop bluetooth support

The bluetooth addon was recently removed by commit
592be1d206e45ad42736b352d96e42ebca50123a, which is why we do not need to
carry the corresponding kernel modules around anymore.

The second version of this patch correctly updates kernel configuration
files via "make oldconfig" as requested by Arne.

Cc: Arne Fitzenreiter <arne.fitzenreiter@ipfire.org>
Cc: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>