Remove deprecated fields from `sso_settings` in App Config.

[lucasmrod]

• SSO setting "Issuer URI" is not used #10257 is removing the "Issuer URI" (sso_settings.issuer_uri) from the UI (no longer needed).
• Remove feature flag that holds 'JIT user set to observer' at creation / first SSO sync #10784 will deprecate the sso_settings.enable_jit_role_sync field.

This issue is to remove both settings sso_settings.issuer_uri and sso_settings.enable_jit_role_sync from the App Config (given that they are not used anymore).

It may require a migration to cleanup the sso_settings in the stored app config JSON.

PS: Do we have to keep backwards compatibility and accept (and ignore) these fields when applying configs?

[zayhanlon]

Thank you @lucasmrod !