Fix ios build

Cannot use errno as method and variable due to conflict with objc

experimental/libbox/setup.go

@@ -35,11 +35,3 @@ func Version() string {
 func FormatBytes(length int64) string {
 	return humanize.IBytes(uint64(length))
 }
-
-type Func interface {
-	Invoke() error
-}
-
-type BoolFunc interface {
-	Invoke() bool
-}