Fix(redshift): unqualify unnest columns

[georgesittas]

Before:

>>> from sqlglot import parse_one
>>> from sqlglot.optimizer.qualify import qualify
>>>
>>> print(qualify(parse_one("SELECT c.f::VARCHAR(MAX) AS f, e AS e FROM a.b AS c, c.d AS e", "redshift"), dialect="redshift", infer_schema=False).sql("redshift", pretty=True))
SELECT
  CAST("c"."f" AS VARCHAR(MAX)) AS "f",
  "_q_0"."e" AS "e"
FROM "a"."b" AS "c", "c"."d" AS   "e"

After:

>>> from sqlglot import parse_one
>>> from sqlglot.optimizer.qualify import qualify
>>>
>>> print(qualify(parse_one("SELECT c.f::VARCHAR(MAX) AS f, e AS e FROM a.b AS c, c.d AS e", "redshift"), dialect="redshift", infer_schema=False).sql("redshift", pretty=True))
SELECT
  CAST("c"."f" AS VARCHAR(MAX)) AS "f",
  "e" AS "e"
FROM "a"."b" AS "c", "c"."d" AS "e"