Currently, the rendering of equations in the speaker notes is problematic: they are rendered both as equations AND texts at the same time. 

```markdown
---
title: Testing equation in speaker note
format: revealjs
---

## Test equation in speaker notes

Sometimes, I want to include some equations in the speaker notes.

::: {.notes}
An equation in display
$$
E = mc^2
$$

or an in-line equation

$E=mc^2$
:::

```
Gives the following in speaker view,

![Speaker view](https://user-images.githubusercontent.com/60116296/161162174-c0704c53-eb33-4bad-834d-213709c337f8.png)


2022-03-31T22:51:27Z
juliantao
closed
[revealjs] Equation in speaker notes
https://github.com/quarto-dev/quarto-cli/issues/494