No need for a [[BackingMap]] in Bluetooth{Manufacturer,Service}DataMap anymore

[rakuco]

See whatwg/webidl#1138 and whatwg/webidl#824. Maplike interfaces no longer need to have a [[BackingMap]] internal slot. Instead, as per https://webidl.spec.whatwg.org/#dfn-map-entries, "Objects implementing an interface that is declared to be maplike represent an ordered map of key–value pairs, initially empty, known as that object’s map entries".

In practice, this means the interface's "map entries" can be referenced and manipulated directly using the standard infra language for ordered maps.