Remove Kore.Internal.OrPattern.toPattern

[ttuegel]

The function toPattern should not exist. Start by removing it from the tests, then from kore-repl, and finally remove it from the main library. This is necessary for #2152.

[ttuegel]

Part of this will be completed in #2623 and part in #2570. The remaining part is to remove it from Kore.Step.Simplification.Iff. When there are multiple children under \iff(_, _), we should expand it to \and(\implies(_, _), \implies(_, _)). The simplifiers for \and and \implies don't use toPattern, so this will take care of it.