iwlwifi: mvm: some clean ups in fw-api-scan.h

Remove unused struct iwl_scan_offload_req and enum
iwl_scan_offload_flags which are not used anymore.  Rename
iwl_scan_offload_schedule to iwl_scan_schedule_lmac to make it clear
that this is for LMAC only.  And fix a small typo.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>