ovsdb: transaction: Remove incorrect transaction abort in pre-commit.

Pre-commit must not abort the transaction, otherwise the upper layers
may crash accessing it.  E.g. ovsdb_trigger_try() checks the state of
the transaction after trying to commit it.

This particular failure can't actually happen, because the function
determine_changes() can't fail.  However, the code is still wrong and
a bit misleading, so should be fixed.

Fixes: 5317898 ("ovsdb: Add support for online schema conversion.")
Acked-by: Mike Pattrick <mkp@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

ovsdb/transaction.c

@@ -1090,7 +1090,6 @@ ovsdb_txn_precommit(struct ovsdb_txn *txn)
      * was really a no-op. */
     error = for_each_txn_row(txn, determine_changes);
     if (error) {
-        ovsdb_txn_abort(txn);
         return OVSDB_WRAP_BUG("can't happen", error);
     }
     if (ovs_list_is_empty(&txn->txn_tables)) {