ovs-ctl: Remove code for upgrading from Open vSwitch 1.6 and earlier.

ovs-ctl: Remove code for upgrading from Open vSwitch 1.6 and earlier.

OVS 1.7 was released in July 2012, so by the time current OVS is released,
it will be almost four years old.  I think that this is long enough to
remove special upgrade code.

It's almost impossible to do this upgrade in any case since there is
no overlap in the base kernel versions supported by the out of tree
modules in the two versions (the only possibility is running the new
version of OVS on the upstream module from Linux 3.3).

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Jesse Gross <jesse@kernel.org>