[pkg-go] Bug#975551: Rename package to just cfssl

[Denis Manente]

Package: golang-cfssl
Version: 1.2.0+git20160825.89.7fb22c8-3
Source: golang-github-cloudflare-cfssl

It seems very unusal to me that this package containing binaries 
consists of the language prefix and as far I can tell the name does not 
conflict or can be confused with another package. This upstream version 
has also been the only been packaged, so it might've been an oversight. 
Packages of other tools written in golang have not that prefix.