x509: drop root_stub.go file (#164)
x509: drop root_stub.go file (#164)

This file is not present in current upstream Go version of
the library, and causes duplicate symbol errors in cross
compilations for darwin. Fixes #159.

The history of this file goes back to the original fork in
2014:
https://github.com/google/certificate-transparency/commit/93f4ead1de06

It was dropped from upstream Go in 1.3 onward, from commit:
https://github.com/golang/go/commit/4f234814831c
daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,RJPercival/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go,daviddrysdale/certificate-transparency-go