octeontx2-af: remove unused cgx_fwi_link_change

The newly added driver causes a warning about a function that is
not used anywhere:

drivers/net/ethernet/marvell/octeontx2/af/cgx.c:320:12: error: 'cgx_fwi_link_change' defined but not used [-Werror=unused-function]

Remove it for now, until a user gets added. If we want to use this
function from another module, we also need a declaration in a header
file, which is currently missing, so it would have to change anyway.

Fixes: 1463f382

 ("octeontx2-af: Add support for CGX link management")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>