net: ethernet: remove fs_mii_disconnect and fs_mii_connect declarations

fs_mii_disconnect and fs_mii_connect have been removed since
commit 5b4b8454

 ("[PATCH] FS_ENET: use PAL for mii management"),
so remove them.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220909062959.1144493-1-cuigaosheng1@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>