wifi: iwlegacy: Remove unused structs and avoid -Wflex-array-member-not-at-end warnings

wifi: iwlegacy: Remove unused structs and avoid -Wflex-array-member-not-at-end warnings

Remove unused structures and avoid the following
-Wflex-array-member-not-at-end warnings:

drivers/net/wireless/intel/iwlegacy/iwl-spectrum.h:68:39: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlegacy/iwl-spectrum.h:60:39: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Link: https://patch.msgid.link/aJl7TxeWgLdEKWhg@kspp
Signed-off-by: Johannes Berg <johannes.berg@intel.com>