counter.go
func (m *CirconusMetrics) RemoveCounterFunc(metric string) {
	m.cfm.Lock()
	defer m.cfm.Unlock()
	delete(m.counterFuncs, metric)
}
func (m *CirconusMetrics) RemoveCounterFunc(metric string) {
	m.cfm.Lock()
	defer m.cfm.Unlock()
	delete(m.counterFuncs, metric)
}
// RemoveCounterFunc removes the named counter function