Duplicate encryption algorithms in extended metadata after config upgrade

Bug description

Duplicate encryption algorithms in extended metadata after config upgrade

How to reproduce the issue

1. In 6.5, create a SAML2 hosted entity
2. Add multiple encryption aliases
3. Do an amster export
4. Run config upgrade
5. Import the upgraded config into 7
6. Check the value of encryption algorithms on hosted entity

Expected behaviour

Set of encryption algorithms to be present with no duplicates

Current behaviour

Contains duplicates