Remove supplementary courses from CS accelerator pages

[croab]

Status

• Current Status: Ready for Review
• Closes https://github.com/NCCE/teachcomputing.org-issues/issues/2716

Review progress:

• Browser tested
• Tech review completed

What's changed?

• Removed the 'View additional courses?' section and much of the supplementary activities logic as it is no longer used anywhere else.

Notes

• This PR assumes that the supplementary courses feature (really a pathway activity) is no longer needed as it is only used in the page section which has been designated for removal. I have, however, left the ability to denote a course as supplementary intact as this is used still by the #recommended_activities method of Pathway. Ideally, we'd just identify all #recommended_activities as just pathway_activities without the boolean supplementary where filter since supplementary courses are no longer used. Pending response to whether we still need to identify supplementary courses at all.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[GDTimi]

Changes look fine on the technical & frontend sides, pending confirmation on the supplementary attribute removal.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud