Revert "iwlwifi: fix build error for CONFIG_IWLAGN=n"

This reverts commit 76232ebf.

iwl_good_ack_health only applies to aggregation and thus only to iwlagn. We
can thus move the function to iwlagn instead of modifying compile flags.
This is done in following patch.
Signed-off-by: NReinette Chatre <reinette.chatre@intel.com>

drivers/net/wireless/iwlwifi/iwl-rx.c

@@ -621,7 +621,6 @@ static void iwl_accumulative_statistics(struct iwl_priv *priv,
 #define BA_TIMEOUT_CNT (5)
 #define BA_TIMEOUT_MAX (16)
 
-#if defined(CONFIG_IWLAGN) || defined(CONFIG_IWLAGN_MODULE)
 /**
  * iwl_good_ack_health - checks for ACK count ratios, BA timeout retries.
  *
@@ -671,7 +670,6 @@ bool iwl_good_ack_health(struct iwl_priv *priv,
 	return rc;
 }
 EXPORT_SYMBOL(iwl_good_ack_health);
-#endif
 
 /**
  * iwl_good_plcp_health - checks for plcp error.