Simplify in-context discussion toggles [BD-38]

[tecoholic]

Description

Implements the following changes:

1. Following toggles will be removed:
   • Allow visibility configuration for each course unit
   • In-context discussion
2. Following toggles will be renamed:
   • "Graded unit pages" will be renamed to "Enable discussions on units in graded subsection"

Testing instructions

1. The test setup uses the demo course setup in devstack and the app running in localhost:2001
2. Change the Discussion provider value to openedx in http://localhost:18000/admin/discussions/discussionsconfiguration/ for the demo course
3. Go to http://localhost:2001/course/course-v1:edX+DemoX+Demo_Course/pages-and-resources/discussion/configure/openedx
4. Check the changes are implemented as expected.

[openedx-webhooks]

Thanks for the pull request, @tecoholic!

When this pull request is ready, tag your edX technical lead.

[codecov]

Codecov Report

Base: 73.89% // Head: 73.95% // Increases project coverage by +0.06% 🎉

Coverage data is based on head (085d6ca) compared to base (8dfac20).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
+ Coverage   73.89%   73.95%   +0.06%     
==========================================
  Files         105      105              
  Lines        1965     1962       -3     
  Branches      475      472       -3     
==========================================
- Hits         1452     1451       -1     
+ Misses        485      484       -1     
+ Partials       28       27       -1     

Impacted Files	Coverage Δ
...app-config-form/apps/openedx/OpenedXConfigForm.jsx	83.78% <ø> (ø)
...fig-form/apps/shared/InContextDiscussionFields.jsx	100.00% <ø> (+33.33%)	⬆️
...-resources/discussions/app-config-form/messages.js	100.00% <ø> (ø)

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[natabene]

@tecoholic Thank you for the contribution, is this ready for our review?

[tecoholic]

@natabene Yes. This is ready for review.
cc: @xitij2000

[xitij2000]

👍 Looks good!

• I tested this: tested on devstack
• I read through the code

[asadazam93]

@xitij2000 Does this have any related Jira ticket?

[natabene]

@asadazam93 No, you will need to create one if you need it.

[openedx-webhooks]

@tecoholic 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.