Over synchronization for read-only index readers in SegmentTermDocs

46	  protected SegmentTermDocs(SegmentReader parent) {
47	    this.parent = parent;
48	    this.freqStream = (IndexInput) parent.core.freqStream.clone();
49	    synchronized (parent) {
50	      this.deletedDocs = parent.deletedDocs;
51	    }
52	    this.skipInterval = parent.core.getTermsReader().getSkipInterval();
53	    this.maxSkipLevels = parent.core.getTermsReader().getMaxSkipLevels();
54	  }