of: mdio: remove of_phy_connect_fixed_link

All in-tree drivers have been converted to use the new pair of
functions: of_is_fixed_phy_link() plus of_phy_register_fixed_link(), we
can now safely remove of_phy_connect_fixed_link.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>