spanner: remove beta notice

Change-Id: Id626b549026a78083a189dc57d71ae3bab4aa93c
Reviewed-on: https://code-review.googlesource.com/c/37170
Reviewed-by: Eno Compton <enocom@google.com>
diff --git a/spanner/doc.go b/spanner/doc.go
index 4954082..72e582b 100644
--- a/spanner/doc.go
+++ b/spanner/doc.go
@@ -19,8 +19,6 @@
 databases. See the packages under admin for clients that operate on databases
 and instances.
 
-Note: This package is in beta. Some backwards-incompatible changes may occur.
-
 See https://cloud.google.com/spanner/docs/getting-started/go/ for an introduction
 to Cloud Spanner and additional help on using this API.