chore: remove a copy-paste error in comment (#2554)

## Overview

A comment contains a stray piece of code at the end, likely from a
copy-paste error.

Author: gap-editor

block/metrics_helpers.go

@@ -50,7 +50,7 @@ func (m *Manager) sendNonBlockingSignalWithMetrics(ch chan<- struct{}, channelNa
 
 // updateChannelMetrics updates the buffer usage metrics for all channels
 func (m *Manager) updateChannelMetrics() {
-	// Update channel buffer usage	if m.metrics.ChannelBufferUsage["header_in"] != nil {
+	// Update channel buffer usage
 	m.metrics.ChannelBufferUsage["header_in"].Set(float64(len(m.headerInCh)))
 
 	m.metrics.ChannelBufferUsage["data_in"].Set(float64(len(m.dataInCh)))