b43legacy: drop ssb-duplicated workaround for dangling cores

Remove the code to detect inactive 802.11 cores, as that function is now done
in ssb.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>