Delete metaData node independent of realtimeExtraction setting

[gjwnc]

If one set's Neos.MetaData.Extractor.realtimeExtraction.enabled to false in Settings.yaml, the signal assetRemoved is not handled. Thus the nodedata table still contains nodes which have properties where the metadata entry is linked to a resource which does not exist any more, e.g. from properties of such a Neos.MetaData:Image node

{
    "assetObject": {
        "__flow_object_type": "Neos\\Media\\Domain\\Model\\Image",
        "__identifier": "033f5153-9089-467b-be6c-55735c69c19b"
    }
    ....

So, this patch is about preventing possible inconsistencies in the nodedata table.

This commit, always handles the signal assetRemoved using ExtractionManager::onAssetRemoved which signals MetaDataCollectionUpdated via Neos\MetaData\MetaDataManager. Thus the asset's metadata node is removed and rebuilding the metadata is also prevented by using onAssetRemoved.

[kdambekalns]

Thanks, sounds very reasonable! I am just not 100% sure about the implementation… so I left some comments.

[gjwnc]

@daniellienert Do you have any concerns to prevent a merge?

I'm using this fix in a fork for two years now and it works well.

[kdambekalns]

@daniellienert To me this seems ok, but I wonder… maybe the whole idea of realtime extraction is to not do anything and instead rely on a cron job or the like to run metadata:extract? So it is in fact intended to have those "dangling links" until an update is explicitly done?