cleanup: deleting duplicate unit test

[pritidesai]

Changes

Deleting a duplicate unit test while validating matrix params. We had a test written twice: https://github.com/tektoncd/pipeline/blob/main/pkg/apis/pipeline/v1/pipeline_types_test.go#L703-L719

/kind cleanup

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs included if any changes are user facing
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  functionality, content, code)
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Release Notes

NONE

[jerop]

thanks @pritidesai!

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[XinruZhang]

/lgtm