Form text input: Remove string refs

[bezalel001]

String refs

e.g ref="textField"

• have issues, see Update nuances of ref callback calling facebook/react#8333 (comment)
• are considered legacy and
• are likely to be removed in one of the future releases
  See https://reactjs.org/docs/refs-and-the-dom.html and
  https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/no-string-refs.md

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