ANDROID: ABI: remove stale symbol

The following symbol was removed by commit c2b6e1a4 ("net: mdio: fix
owner field for mdio buses registered using device-tree"). It also needs
to be removed from this symbol list to reflect this update.

- of_mdiobus_register

Bug: 277759776
Change-Id: I4ab79a86f13404c2d0b2e423154aaa8b512bc1c4
Signed-off-by: Carlos Llamas <cmllamas@google.com>