Remove use of 'shallow' (react-unit-test-utils) in following components/files:

• [src/containers/ResponseDisplay/PreviewDisplay.test.jsx]
• [src/containers/ResponseDisplay/SubmissionFiles.test.jsx]
• [src/containers/ResponseDisplay/components/FileExtensionCell.test.jsx]
• [src/containers/ResponseDisplay/components/FileNameCell.test.jsx]
• [src/containers/ResponseDisplay/index.test.jsx]