Improve DeleteSubjectJob when run as DeferredJob

The deletion job was forced to neglect historic data (Store has no knowledge of any revision data), where it solely depended on the Store's data fetch at the time of execution which influenced as to when to schedule the update and removal.

SMW 1.9 deployes a SemanticData serializer/deserializer which enables to serialize SemanticData at any time and can be used before the subject and its data are removed.

Running [1] the serializer adds a diminutive overhead during the deletion process which enables to delete a subject immediately without delay but enables to schedule the dispatch and refresh associative entities as deferred job [2].

[1] 'smwgDeleteSubjectWithAssociatesRefresh' => true
[2] 'smwgDeleteSubjectAsDeferredJob' => true