Remove use of the assessmentmetadata state mapper

[rtibbles]

The AssessmentMetadataState mapper was introduced when the ContentNode API returned a singleton array of assessmentmetadata. It now returns a null value or a single object.

Unfortunately, there are several places where this is still used, rather than directly reading from the expected return shape of the API endpoint.

### Acceptance criteria:
- [x] Enumerate all places where the state mapper is used in this issue
- [x] Find all the places 'downstream' of these places where the content node assessment metadata is referenced
- [x] Update these to read directly from the shape of assessmentmetadata as returned by the API (see the JSDoc for this here: https://github.com/learningequality/kolibri/blob/release-v0.16.x/kolibri/core/assets/src/api-resources/contentNode.js#L64)

[a6ar55]

I would like to work on this

[AlexVelezLl]

Hi @a6ar55! Sure! I will assign this issue to you :open_hands:.

[nick2432]

The current assignee is not active; can i work on this task?

[MisRob]

Hi @nick2432, thanks for volunteering. Let's wait a day or two for @a6ar55 to confirm whether they're working on it or no. Then we can possibly re-assign.

[a6ar55]

Hi @MisRob , Unfortunately, I am unable to work on this issue at the moment. Therefore, please feel free to reassign the task to @nick2432.

[MisRob]

Thanks for letting us know, @a6ar55. I am re-assigning to @nick2432.

[AymanHammadi]

I'd like to work on this issue. Could you please assign it to me?

Also I have a question about mastery_model values: After the removal of the assessmentMetaDataState mapper, should we assume these values will always be in snake_case format? Currently, this mapper ensures snake_case. I just want to make sure I understand it correctly.

[rtibbles]

Yes, the assessment metadata will now be accessed in the same way as it is returned from the API for resource metadata. The JSDoc types for this can be found here: https://github.com/learningequality/kolibri/blob/develop/kolibri/core/assets/src/api-resources/contentNode.js#L18 (see below in the same file for how to access this from the ContentNode metadata).

[rtibbles]

Assigned!

[rtibbles]

Fixed in #11940