[FileUpload] Remove outdated lifecycle methods and fix issue with stale state

[AndrewMusgrave]

WHY are these changes introduced?

• Removes outdated lifecycle method
• fixes a bug that keep default action title / hint when removed

WHAT is this pull request doing?

Taking advantage of getDerivedStateFromProps and adding additional logic to handle the bug fix

How to 🎩

Is my logic 🔉 ? Try examples and playground code (on master) - see how after the original default hint and title are shown, they won't show again after you set a hint / title. Even when removed.

Copy-paste this code in playground/Playground.tsx:

import * as React from 'react';
import {
  Page,
  TopBar,
  Layout,
  SettingToggle,
  ContextualSaveBar,
  TextStyle,
  Frame,
  AppProvider,
  DropZone,
  Button,
} from '../src';

interface State {}

export default class ProviderThemeExample extends React.Component {
  actionTitle = 'Action Title';
  actionHint = 'Action Hint';
  state = {
    actionTitle: this.actionTitle,
    actionHint: this.actionHint,
  };

  render() {
    const {actionHint, actionTitle} = this.state;

    return (
      <>
        <DropZone>
          <DropZone.FileUpload
            actionHint={actionHint}
            actionTitle={actionTitle}
          />
        </DropZone>
        <Button
          onClick={() => {
            this.setState({
              actionTitle:
                actionTitle === this.actionTitle ? undefined : this.actionTitle,
              actionHint:
                actionHint === this.actionHint ? undefined : this.actionHint,
            });
          }}
        >
          Change hint and title
        </Button>
      </>
    );
  }
}

[elileto]

Tophatted on multiple browsers and mobile. looks guuud.