Items removed from 'external-ids' or 'other-config' in the Open_vSwitch table are not removed from operational MD-SAL

OVSDB updates to the Open_vSwitch table which include deletions from the 'external-ids' or 'other-config' columns are not updated in the MD-SAL.

Example:
On the OVSDB node, add someething to 'external-ids':

1. sudo ovs-vsctl set open_vswitch . external-id:hello=there

As a result, the "hello,there" entry will be added to the OVSDB southbound
operational MD-SAL datastore for the associated OVSDB node.

Now, remove the entry from the OVSDB node:

1. sudo ovs-vsctl remove open_vswitch . external-id "hello"

While the "hello,there" entry is removed from the Open_vSwitch table in the
OVSDB on the OVSDB Node (check with # sudo ovs-vsctl list open_vswitch), the OVSDB southbound operational MD-SAL datastore
will still contain the "hello,there" entry.