asset-hubs: simplify xcm-config (#6222)
`ForeignCreatorsSovereignAccountOf` is used by `ForeignCreators` filter
to convert location to `AccountId`, _after_ `ForeignCreators::IsForeign`
filter passes for an (asset, location) pair.
The `IsForeign` filter is the actual differentiator, so if a location
passes it, we should support converting it to an `AccountId`.
As such, this commit replaces `ForeignCreatorsSovereignAccountOf`
converter with the more general `LocationToAccountId` converter.
Signed-off-by: Adrian Catangiu <[email protected]>