fix: [microbatch] delete redundant using clause

[ugmuka]

resolves #1198

Problem

The microbatch feature generates a DELETE SQL statement that includes a redundant USING clause. The current SQL looks like this:

delete from <target_model_name> DBT_INTERNAL_TARGET
    using <tmp_table>
    where (
    DBT_INTERNAL_TARGET.event_date >= TIMESTAMP '2024-10-13 00:00:00+00:00'
    and DBT_INTERNAL_TARGET.event_date < TIMESTAMP '2024-10-14 00:00:00+00:00'

    );

This results in a Cartesian join, which is unnecessary. To resolve this issue, the USING clause should be removed.

Solution

Remove the USING clause from merge.sql.

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [x] I have run this code in development and it appears to resolve the stated issue
• [x] This PR includes tests, or tests are not required/relevant for this PR
• [x] This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

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[ugmuka]

I have signed CLA.

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