Gigasecond exercise - removes irrelevant comment
Gigasecond exercise - removes irrelevant comment

The PR #222 removed the Birthday variable from
the test code, however the comment was not
removed which is very confusing. This commit
simply removes the comment.

leenipper/xgo,exercism/xgo,exercism/xgo,robphoenix/exercism-go,leenipper/xgo,robphoenix/exercism-go