Remove tmp file after test passed

[bbroeksema]

resolves 5631

Description

This pull request improves a test case by removing a tmp file that is created during test execution. The resolution has been verified by following the steps to reproduce as described in: #5631 and verifying that after this fix the file is indeed removed. This PR adds the rm_file from dbt.tests.utils to remove the specific file.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry

I haven't add a changelog entry yet, does that make sense for fixing a test?

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Bertjan Broeksema.
This is most likely caused by a git client misconfiguration; please make sure to:

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[bbroeksema]

I've added the email address which I used to sign the CLA to my github account. Do I need to to anything else to make the check pass?

[gshank]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[jtcohen6]

@bbroeksema Could you add a changelog entry? We don't usually require one for changes to tests only, but it's also our way of giving you credit for your contribution :)

[bbroeksema]

@jtcohen6 done.