mu4e: mappings not available when (modulep! +org)

### I confirm that...

- [x] I searched the issue tracker and found no similar issues.

- [x] I searched the [documentation](https://docs.doomemacs.org), [FAQ](https://docs.doomemacs.org/-/faq), [discussion board](https://doomemacs.org/discuss), and [Google](https://google.com) for solutions to my issue.

- [x] I read [the debugging guide](https://doomemacs.org/d/how2debug) and researched the issue to the best of my ability.

- [x] My issue can be observed on the latest available commit of Doom.

- [x] My issue can be observed on a stable release of Emacs (i.e. doesn't end in `.50`, `.60`, or `.90`–`.99`)

### Describe your issue

When I enable `+org` in mu4e:

``` elisp
:email
(mu4e
+org
+mbsync)
```

I'd expect to still have mappings for `message-send-and-exit`, `message-dont-send`, `+mu4e/attach-files`... through `SPC m `
https://github.com/doomemacs/doomemacs/blob/master/modules/email/mu4e/config.el#L357-L362

But it seems those mappings are no longer available when `org-msg` module is loaded. Only `+mu4e/attach-files` is accessible.
https://github.com/doomemacs/doomemacs/blob/master/modules/email/mu4e/config.el#L422

### Steps to reproduce

0. Enable `(mu4e +org)`
1. `SPC o m` to enter mu4e
2. `C` to compose new email
3. `SPC m`

### System information

https://gist.github.com/wchmb/6c89461388917f7f9057484c71ba8623