Please make `write_eml()` defunct (rather than just removing it)

- [ ] Make `write_eml()` defunct just like `write_dwc()`
- [ ] Return for both that it is defunct.
- [ ] Suggest the camtrapdp alternative for both


```R
> write_eml()
Error in write_eml() : could not find function "write_eml"

> write_dwc()
Error:
! `write_dwc()` was deprecated in camtraptor 1.0.0 and is now defunct.
Run `rlang::last_trace()` to see where the error occurred.
```