build: drop support for go1.8

backend/drive/drive.go

@@ -1,7 +1,4 @@
 // Package drive interfaces with the Google Drive object storage system
-
-// +build go1.9
-
 package drive
 
 // FIXME need to deal with some corner cases

backend/drive/drive_internal_test.go

@@ -1,5 +1,3 @@
-// +build go1.9
-
 package drive
 
 import (

backend/drive/drive_test.go

@@ -1,7 +1,5 @@
 // Test Drive filesystem interface
 
-// +build go1.9
-
 package drive
 
 import (

backend/drive/drive_unsupported.go

@@ -1,6 +0,0 @@
-// Build for unsupported platforms to stop go complaining
-// about "no buildable Go source files "
-
-// +build !go1.9
-
-package drive

backend/drive/upload.go

@@ -8,8 +8,6 @@
 //
 // This contains code adapted from google.golang.org/api (C) the GO AUTHORS
 
-// +build go1.9
-
 package drive
 
 import (