selftests: mlxsw: Remove deprecated test

The addition of a VLAN on a bridge slave prompts the driver to have the
local port in question join the FID corresponding to this VLAN.

Before recent changes, the operation of joining the FID would also mean
that the driver would enable VXLAN tunneling if a VXLAN device was also
member in the VLAN. In case the configuration of the VXLAN tunnel was
not supported, an extack error would be returned.

Since the operation of joining the FID no longer means that VXLAN
tunneling is potentially enabled, the test is no longer relevant. Remove
it.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>