Fix mistake in usage drop_constraint parameters

In migration e197124d4b9_add_unique_constrain mistake in usage
drop_constraint parameter type_ and positional arguments name
and table_name.

The same mistake was already fixed in migration
63afba73813_ovs_tunnelendpoints_id_unique.

Change-Id: I6a250e55ea53048bb11afd71fecf94da6f0c7421
Closes-bug: #1257607
Merge "Fix mistake in usage drop_constraint parameters"