remove stale.ymal file

[victoriacheng15]

Fixes Issue

Close #694

Changes proposed

Check List (Check all the applicable boxes)

• [] My code follows the code style of this project.
• [] My change requires changes to the documentation.
• [] I have updated the documentation accordingly.
• [x] All new and existing tests passed.
• [x] This PR does not contain plagiarized content.
• [x] The title of my pull request is a short description of the requested changes.

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