fix: Fix old migrations for Keto 0.8, column nit is not exists in table network

[DarkDrim]

Updated old migrations (for update between keto 0.7 and 0.8)
Table networks don't have column nit:

So correct query should be

DELETE FROM keto_relation_tuples WHERE nid NOT IN (SELECT id FROM networks);

I've faced this issue when migrate Keto from 0.7 to 0.8:

20220217152313000000  nid_fk    Pending  
Applying migrations...
Could not apply migrations: ERROR: insert or update on table "keto_relation_tuples" violates foreign key constraint "keto_relation_tuples_nid_fk" (SQLSTATE 23503)
error executing migrations/sql/20220217152313000000_nid_fk.up.sql, sql: -- These tuples can't be retrieved over any API (and also not inserted by any API) because we always add a WHERE nid = ? clause to the queries.
-- This DELETE statement is here to ensure that we don't run into problems where the nid column is not properly set. Should not happen if only the official API is used.
DELETE FROM keto_relation_tuples WHERE nid NOT IN (SELECT nid FROM networks);

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