Fix AppVeyor unit tests for code refactoring

[DonJayamanne]

1) Method Extraction "before each" hook for "Extract Method will fail if complete statements are not selected":
6204     Error: EBUSY: resource busy or locked, unlink 'C:\projects\vscode-python-v3vd6\out\test\pythonFiles\refactoring\standAlone\refactor.py'
6205      at Object.fs.unlinkSync (fs.js:1091:18)
6206      at Object.<anonymous> (C:\projects\vscode-python-v3vd6\src\test\refactor\extension.refactor.extract.method.test.ts:42:16)
6207      at Generator.next (<anonymous>)
6208      at fulfilled (C:\projects\vscode-python-v3vd6\out\test\refactor\extension.refactor.extract.method.test.js:5:58)
6209      at <anonymous>
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