[Blackfin] arch: fix bug gdb testing on hardware has regression

http://blackfin.uclinux.org/gf/project/toolchain/tracker/?action=TrackerItemEdit&tracker_item_id=3651

As Bernd predicted, this was only necessary because of other
problems in the kenel - fixing those, and this is not necessary, so
remove it.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>