[PM-6606] remove onboarding feature flag

[merissaacosta]

Type of change

- [ ] Bug fix
- [ ] New feature development
- [x] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

Removes the vault onboarding feature flag since that project is live now.

Code changes

• src/Core/Constants.cs removes VaultOnboarding

Before you submit

• Please check for formatting errors (dotnet format --verify-no-changes) (required)
• If making database changes - make sure you also update Entity Framework queries and/or migrations
• Please add unit tests where it makes sense to do so (encouraged but not required)
• If this change requires a documentation update - notify the documentation team
• If this change has particular deployment requirements - notify the DevOps team

[merissaacosta]

@Jingo88 do we need to wait to merge this after the client is released without the flag?

[github-actions]

LaunchDarkly flag references

❌ 1 flag removed

Name	Key	Aliases found	Info
Vault Onboarding	vault-onboarding		✅ all references removed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 38.66%. Comparing base (fd173e8) to head (e4303bd).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4085   +/-   ##
=======================================
  Coverage   38.66%   38.66%           
=======================================
  Files        1209     1209           
  Lines       58561    58561           
  Branches     5594     5594           
=======================================
  Hits        22643    22643           
- Misses      34863    34864    +1     
+ Partials     1055     1054    -1     

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[github-actions]

Checkmarx One – Scan Summary & Details – 84f66ca8-fc5b-46d6-b46a-de9fcb0978d2

No New Or Fixed Issues Found