sys: move ForceRemoveAll to integration/client

ForceRemoveAll was only used in tests/fuzzing, but added hcsshim as dependency
for the sys package. Moving this to integration/client makes the "sys" package
slightly more lightweight, and may help simplifying dependency-management.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

integration/client/helpers_unix.go

@@ -0,0 +1,27 @@
+//go:build !windows
+// +build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package client
+
+import "os"
+
+// forceRemoveAll on unix is just a wrapper for os.RemoveAll
+func forceRemoveAll(path string) error {
+	return os.RemoveAll(path)
+}