net: dsa: Remove adjust_link paths

Now that we no longer any drivers using PHYLIB's adjust_link callback,
remove all paths that made use of adjust_link as well as the associated
functions.

Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20240430164816.2400606-3-florian.fainelli@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>