Revert "Remove unused utility function StringInSplice."

This reverts commit 43b0f2d925.

kustomize/internal/commands/kustfile/kustomizationfile.go

@@ -176,6 +176,16 @@ func (mf *kustomizationFile) Write(kustomization *types.Kustomization) error {
 	return mf.fSys.WriteFile(mf.path, data)
 }
 
+// StringInSlice returns true if the string is in the slice.
+func StringInSlice(str string, list []string) bool {
+	for _, v := range list {
+		if v == str {
+			return true
+		}
+	}
+	return false
+}
+
 func (mf *kustomizationFile) parseCommentedFields(content []byte) error {
 	buffer := bytes.NewBuffer(content)
 	var comments [][]byte