phylib: remove unused adjust_state() callback

Remove adjust_state() callback from 'struct phy_device' since it seems to have
never been really used from the inception: phy_start_machine() has been always
called with 2nd argument equal to NULL.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>