classifier: Remove rare optimization case.

classifier: Remove rare optimization case.

This optimization applied when a staged lookup index would narrow down
to a single rule, which happens sometimes is simple test cases, but
presumably less often in more populated flow tables.  The result of
this optimization allowed a bit more general megaflows, but the bit
patterns produced were sometimes cryptic.  Finally, a later fix to a
more important performance problem does not allow for this
optimization any more, so remove it now.

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Ryan Moats <rmoats@us.ibm.com>
Acked-by: Ben Pfaff <blp@ovn.org>