Revert "pvector: Expose non-concurrent priority vector."

Revert "pvector: Expose non-concurrent priority vector."

This reverts commit 8bdfe1313894047d44349fa4cf4402970865950f.

I failed to see that lib/dpif-netdev.c actually needs the concurrency
provided by pvector prior to this change.  More specifically, when a
subtable is removed, concurrent lookups may skip over another subtable
swapped in to the place of the removed subtable in the vector.

Since this was the only use of the non-concurrent pvector, it is
cleaner to revert the whole patch.

Reported-by: Jan Scheurich <jan.scheurich@ericsson.com>
Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Daniele Di Proietto <diproiettod@vmware.com>