1.6.2 Latency issue, reverting the RequestCounter to Histogram

When Search PTS client was canaried with 1.6.2 we saw 10x latency
spikes. The logs contain contention error message below
"addRequest lost timing instrumentation data because three retries was
insufficient to update the accumulator."

So in this fix, we are canarying reverting the RequestCounters back
to Histogram. The new syncOpTime and asyncOpTime counters are ignored
and will always return 0.