i40e: Deprecating unused macro

I40E_MAC_X710 was supposed to be for 10G and I40E_MAC_XL710
was supposed to be for 40G. But function i40e_is_mac_710
sets I40E_MAC_XL710 for all device IDS, I40E_MAC_X710 is not
used at all. As there is nothing to compare there is no need
for this function. Thus deprecating this extra macro and
removing this function entirely and replacing it with a direct
check.

Change-ID: I7d1769954dccd574a290ac04adb836ebd156730e
Signed-off-by: Bimmy Pujari <bimmy.pujari@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>