docs(pubsublite): promote pubsublite to stable (#4301)

Remove comments about Beta status from docs.

Release-As: 1.0.0
diff --git a/pubsublite/README.md b/pubsublite/README.md
index 9d3ee9d..5c7123f 100644
--- a/pubsublite/README.md
+++ b/pubsublite/README.md
@@ -6,8 +6,6 @@
 - [Go client documentation](https://pkg.go.dev/cloud.google.com/go/pubsublite)
 - [Complete sample programs](https://github.com/GoogleCloudPlatform/golang-samples/tree/master/pubsublite)
 
-*This library is in BETA. Backwards-incompatible changes may be made before
- stable v1.0.0 is released.*
 
 ### Example Usage
 
diff --git a/pubsublite/doc.go b/pubsublite/doc.go
index 3ec736d..cb71469 100644
--- a/pubsublite/doc.go
+++ b/pubsublite/doc.go
@@ -32,9 +32,6 @@
 See https://pkg.go.dev/cloud.google.com/go for authentication, timeouts,
 connection pooling and similar aspects of this package.
 
-Note: This library is in BETA. Backwards-incompatible changes may be made before
-stable v1.0.0 is released.
-
 
 Introduction