Switch cfhistograms from using yammer metrics in 2.1

cfhistograms was changed to use the yammer histograms CASSANDRA-5871. Until CASSANDRA-5657's change to metrics we shouldn't represent the yammer histogram for latency metrics. Yammer's histogram is based on assumption of a normal distribution and is bad at representing the tail percentiles with skewed distributions. So revert the change just in the 2.1 branch but leave it for 3.0.