crypto/internal/hpke: use internal/byteorder instead of encoding/binary

crypto/internal/hpke: use internal/byteorder instead of encoding/binary

crypto/internal/hpke is the only package under crypto that imports
encoding/binary. Other packages use internal/byteorder instead, which
notably doesn't depend on the reflect package.

Updates #54097

Change-Id: I77a3ac5f4588527a2f82574df4cb84d30630d73f
Reviewed-on: https://go-review.googlesource.com/c/go/+/622497
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>