net: dsa: tag_8021q: remove old comment regarding dsa_8021q_netdev_ops

Since commit 129bd7ca ("net: dsa: Prevent usage of NET_DSA_TAG_8021Q
as tagging protocol"), dsa_8021q_netdev_ops no longer exists, so remove
the comment that talks about it.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20220818143808.2808393-1-vladimir.oltean@nxp.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>