Removing the CancelSessionUpliftJourney feature flag

[ste-banks]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Checklist:

• My work is behind a feature toggle (if appropriate)
• If my work is behind a feature toggle, I've added a full suite of tests for both the ON and OFF state
• The ticket number is in the Pull Request title, with format "APPT-XXX: My Title Here"
• I have ran npm tsc / lint (in the future these will be ran automatically)
• My code generates no new .NET warnings (in the future these will be treated as errors)
• If I've added a new Function, it is disabled in all but one of the terraform groups (e.g. http_functions)
• If I've added a new Function, it has both unit and integration tests. Any request body validators have unit tests also
• If I've made UI changes, I've added appropriate Playwright and Jest tests
• If I've added/updated an end-point, I've added the appropriate annotations and tested the Swagger documentation reflects the change

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud