Remove archive/stat_unsupported.go because it is not used

LUtimesNano and all other functions were implemented on pkg/system after
d6114c0da0e844199e3d23c60a04434566fb5392.

Docker-DCO-1.1-Signed-off-by: Kato Kazuyoshi <kato.kazuyoshi@gmail.com> (github: kzys)

archive/stat_unsupported.go

@@ -1,21 +0,0 @@
-// +build !linux !amd64
-
-package archive
-
-import "syscall"
-
-func getLastAccess(stat *syscall.Stat_t) syscall.Timespec {
-	return syscall.Timespec{}
-}
-
-func getLastModification(stat *syscall.Stat_t) syscall.Timespec {
-	return syscall.Timespec{}
-}
-
-func LUtimesNano(path string, ts []syscall.Timespec) error {
-	return ErrNotImplemented
-}
-
-func UtimesNano(path string, ts []syscall.Timespec) error {
-	return ErrNotImplemented
-}