iwlagn: remove 6000 hw header

The constants can be moved together with
the similar ones for other devices and we
can then remove the file.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>