histogram.go
func (m *CirconusMetrics) RemoveHistogram(metric string) {
	m.hm.Lock()
	delete(m.histograms, metric)
	m.hm.Unlock()
}
func (m *CirconusMetrics) RemoveHistogram(metric string) {
	m.hm.Lock()
	delete(m.histograms, metric)
	m.hm.Unlock()
}
// RemoveHistogram removes a histogram