github/codeql-go is being merged into github/codeql.
Update references to `codeql-go` within the CodeQL CLI docs.
Add Go to the list of mentioned languages where applicable.
Leave an explanatory note in the setup instructions about the
previous requirement to check out `github/codeql-go`, and
mention this is no longer necessary.
The remaining references are to historical commits,
which will continue to exist.
