xAODBTagging: Threading cleanups.
toPersistent is no longer needed; null out the body of BTagging_v1::toPersistent.
Also null out the non-reentrant functions associated with it, and remove the static variables.
toPersistent is no longer needed; null out the body of BTagging_v1::toPersistent.
Also null out the non-reentrant functions associated with it, and remove the static variables.