[EC-400] Code clean up Device Verification

[fedemkr]

Type of change

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

Objective

Remove the code introduced by Device Verification feature.
Related PRs:

• Email verification for new devices #1931
• [PS-82] Check Send 2FA email for login for new devices #1977
• EC-198 Added feature flag for 2FA Email for new device login #1993
• [PS-589] Fix emergency contact takeover device verification and endpoints for its settings #2016
• [PS-589] Fix DeviceUnknownVerification User_Update proc #2041
• [EC-293] Fix device verification get settings so the state is correct #2094
• [EC-309] Change Device Verification default global setting value to false #2106
• [EC-309] Fix build on Device Verification default global flag change #2112

Code changes

• TwoFactorController: I was in doubt here whether to remove the endpoints, so I just marked them as obsolete and changed them to return a default value. These endpoints were being used in the web client but were removed in this PR. Leaving them here in case a self hosted instance has an old version of the web client. LMK if I should just remove them or change something else
• DeviceVerificationRequestModel, DeviceVerificationResponseModel: I left these model just because of the obsolete endpoints aforementioned. LMK if I should remove them as well.
• Database changes: Removed the column UnknownDeviceVerificationEnabled from the User table.
• others: Removed code introduced by the aforementioned PRs

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

[jlf0dev]

Everything looks good to me! Sad to see all that effort go, but at least the 2f code looks a little cleaner now 👍