examples/ct: drop extra return val from serializeAndSignSCT
examples/ct: drop extra return val from serializeAndSignSCT

The leaf input is returned unmodified, so drop it as a return value to
make this clear.

RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go,daviddrysdale/certificate-transparency-go,daviddrysdale/certificate-transparency-go,google/certificate-transparency-go