net: wwan: iosm: remove unused macro definition

IOSM_IF_ID_PAYLOAD is defined but not used.
Remove it to avoid unexpected usage.
Signed-off-by: M Chetan Kumar <m.chetan.kumar@linux.intel.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/0697e811cb7f10b4fd8f99e66bda1329efdd3d1d.1683649868.git.m.chetan.kumar@linux.intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/wwan/iosm/iosm_ipc_wwan.c

@@ -18,8 +18,6 @@
 #define IOSM_IP_TYPE_IPV4 0x40
 #define IOSM_IP_TYPE_IPV6 0x60
 
-#define IOSM_IF_ID_PAYLOAD 2
-
 /**
  * struct iosm_netdev_priv - netdev WWAN driver specific private data
  * @ipc_wwan:	Pointer to iosm_wwan struct