chore: remove concurrency tools from helpers (#86)

## Description
Zarf was the only user of these tools, but we have since refactored our
code to use `errgroups` rather than `ConcurrencyTools`


https://github.com/defenseunicorns/zarf/pull/2460/files#diff-efb99da1ff0c60478a053ac9f6acfa8eba6237adc87cd430cdbf3b5a32d1b16c

## Related Issue

Fixes #70

Author: Lucas Rodriguez

helpers/concurrency.go

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-FileCopyrightText: 2024-Present Defense Unicorns
 
+// Package helpers provides common helper functions for Go.
 package helpers
 
 import (