Remove builds conditional on go1.7 since that is now guaranteed #2154

Old fallback code was deleted and the go1.7 style code inlined where
appropriate.

backend/azureblob/azureblob.go

@@ -1,7 +1,4 @@
 // Package azureblob provides an interface to the Microsoft Azure blob object storage system
-
-// +build go1.7
-
 package azureblob
 
 import (