net: packetengines: remove obsolete yellowfin driver and vendor dir

net: packetengines: remove obsolete yellowfin driver and vendor dir

Similar to the hamachi driver, the yellowfin driver supports hardware
that is over two decades old and no longer in active use.

Since yellowfin was the last remaining driver in the packetengines
vendor directory, we can now safely remove the entire directory and
drop its associated references from the parent Kconfig and Makefile.

This eliminates dead code and reduces the overall maintenance burden
on the netdev subsystem.

Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260422044820.485660-3-25181214217@stu.xidian.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>