Drop Message.SNS
Correct Topic.Delete() test

Topics need a related SNS field to know which endpoint to hit for the request.
Pass message around as a string, not an 8192-byte
Set Topic.SNS in sns.CreateTopic()
Set Topic.SNS in sns.ListTopics
go fmt in Topic.Delete()
Drop Message.SNS
Merge pull request #86 from radar/sns-cleanup-2

More SNS Cleanup