dbt-materialize: Stop adding aliases to subqueries with --empty

[bobbyiliev]

Motivation

As per this bug here, the --empty flag doesn't work with relations that are aliased and fails.

A quick repro:

• Create a simple model with: SELECT * FROM {{ ref('my_upstream_model')}} some_alias
• The generated SQL when using the --empty flag, looks like this:

as (
  SELECT * FROM (
    select * from "my_upstream_model" where false limit 0) _dbt_limit_subq_my_upstream_model alias
);

Tips for reviewer

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• This PR includes the following user-facing behavior changes:

[benesch]

Nice, good find.