Remove default template headers of Hierarchy and Type Parameters from DefaultThemeRenderContext when overridden.

[kaphula]

If you create your own theme by extending DefaultThemeRenderContext and attempt to override this.hierarchy or this.typeParameters with empty content (disable them), their HTML headers get generated to the output document regardless. This PR removes the HTML headers if the default template is overridden.

export class FooterOverrideThemeContext extends DefaultThemeRenderContext {
  constructor(theme: DefaultTheme, options: Options) {
    super(theme, options);
    // disable:
    this.hierarchy = () => { return (<></>)}
    this.typeParameters = () => { return(<></>)}
  }
}

[Gerrit0]

Any reason the <section> (and maybe even the condition) didn't move into the helpers? Seems like you'd still have elements you don't want if modifying these helpers.

[Gerrit0]

Thanks!