Switch off BitSet for tracking referenced static entries.

Since the static reference set has <64 entries, we can use a long to track emission.  This saved 2 allocations and 48 bytes decompression overhead.

```
# before
Starting experiment 3 of 18: {instrument=allocation, benchmarkMethod=decodeIndexedHeaderFieldFromStaticTableWithoutBufferingOkHttp, vm=default, parameters={}}… Complete!
  bytes(B): min=600.00, 1st qu.=600.00, median=600.00, mean=600.00, 3rd qu.=600.00, max=600.00
  objects: min=13.00, 1st qu.=13.00, median=13.00, mean=13.00, 3rd qu.=13.00, max=13.00
# after
Starting experiment 3 of 18: {instrument=allocation, benchmarkMethod=decodeIndexedHeaderFieldFromStaticTableWithoutBufferingOkHttp, vm=default, parameters={}}… Complete!
  bytes(B): min=552.00, 1st qu.=552.00, median=552.00, mean=552.00, 3rd qu.=552.00, max=552.00
  objects: min=11.00, 1st qu.=11.00, median=11.00, mean=11.00, 3rd qu.=11.00, max=11.00
```