Documentation: net: phy: remove description of function pointers

Remove the function pointers documentation which duplicates information
found in include/linux/phy.h. Maintaining documentation about two
different locations just does not work, but the code is less likely to
be outdated.

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>