net: delete __dev_getfirstbyhwtype

The last user of the RTNL brother of dev_getfirstbyhwtype (the latter
being synchronized under RCU) has been deleted in commit b4db2b35
("afs: Use core kernel UUID generation").

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20201129200550.2433401-1-vladimir.oltean@nxp.com


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