Remove use of appenginevm build tag.

Managed VM apps can use the net/http package directly, and can use the
metadata server instead of the appengine package to get Service Account
tokens.

Change-Id: Ifa30eea446ffe4a9121ce3401900f4b73ddf07db
Reviewed-on: https://go-review.googlesource.com/14125
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/client_appengine.go b/client_appengine.go
index 4a554cb..52f8d1d 100644
--- a/client_appengine.go
+++ b/client_appengine.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build appengine appenginevm
+// +build appengine
 
 // App Engine hooks.
 
diff --git a/google/appengine_hook.go b/google/appengine_hook.go
index 2f9b154..362766f 100644
--- a/google/appengine_hook.go
+++ b/google/appengine_hook.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build appengine appenginevm
+// +build appengine
 
 package google