Drop dependency from certificate-transparency-go

[pav-kv]

Currently, there is a circular dependency between trillian and certificate-transparency-go modules:

~/go/src/github.com/google/trillian$ go mod graph | grep " github.com/google/certificate-transparency-go"
github.com/google/trillian github.com/google/[email protected]
github.com/google/[email protected] github.com/google/[email protected]
github.com/google/[email protected] github.com/google/[email protected]

In the reverse direction:

~/go/src/github.com/google/certificate-transparency-go$ go mod graph | grep " github.com/google/trillian"
github.com/google/certificate-transparency-go github.com/google/[email protected]
github.com/google/[email protected] github.com/google/[email protected]
github.com/google/[email protected] github.com/google/[email protected]

The only used package from certificate-transparency-go repository is tls serialisation format imported here.

[mhutchinson]

https://go-proverbs.github.io: A little copying is better than a little dependency

Just copy tls into an internal directory inside trillian? :-)