Update base64_amd64.go

[lantuin]

goost.org doesn't work

[gen2brain]

The solution is to use github.com/libgoost/encoding-base64, what you did is just duplicate the same file as is in base64.go, you could just remove base64_amd64.go then.The library is base64 implementation in assembler and it improves performance on amd64, I would like to continue using it.