Issue #347 : Add remove button to default file input previews

[nicoledow]

Description

V6 adds support for multiple files in the FileInput component, with each file having a remove button. This PR is meant to provide that same remove button when the multiple prop is false. Clicking the "x" sets the value back to an empty string.

Author Checklist

• [ ] Add unit test(s)
• [ ] Update version in package.json (see the versioning guidelines)
• [ ] Update documentation (if necessary)
• [ ] Add story to storybook (if necessary)
• [ ] Assign dev reviewer

[chawes13]

@nicoledow Thanks! Could you update the documentation via the JS doc comments on line 37 and 39 in file-input.js? The docs.md file should be updated automatically via pre-commit. If for some reason that doesn't work, you can run yarn docs manually.

[nicoledow]

@chawes13 docs updated ✅