classifier: Remove OF1.0 special case from classifier_find_rule_exactly().
This special case should never have actually triggered in practice, because
OpenFlow 1.0 cannot set up an exact-match rule as defined by
flow_wildcards_is_exact(). (OpenFlow 1.0 will always, for example,
wildcard all NXM registers.)
OVS implements this OF1.0 special case differently, by changing flow
priority to 65535 in cls_rule_from_match() if the flow is an exact match as
defined by OpenFlow 1.0.