Teach RemoveRoleFromObjectPolicy() about partitioned tables.

Table partitioning, introduced in commit f0e44751, added a new
relkind - RELKIND_PARTITIONED_TABLE. Update
RemoveRoleFromObjectPolicy() to handle it, otherwise DROP OWNED BY
will fail if the role has any RLS policies referring to partitioned
tables.

Dean Rasheed, reviewed by Amit Langote.

Discussion: https://postgr.es/m/CAEZATCUnNOKN8sLML9jUzxecALWpEXK3a3W7y0PgFR4%2Buhgc%3Dg%40mail.gmail.com