expr/v1alpha1: deprecate and stop generation

Change-Id: I998a52034494f0d7e994e0169936136dac9a7857
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/55091
Reviewed-by: Cody Oss <codyoss@google.com>
Reviewed-by: Tristan Swadell <tswadell@google.com>
Reviewed-by: kokoro <noreply+kokoro@google.com>
diff --git a/expr/apiv1alpha1/doc.go b/expr/apiv1alpha1/doc.go
index 2fe6ece..b54372a 100644
--- a/expr/apiv1alpha1/doc.go
+++ b/expr/apiv1alpha1/doc.go
@@ -31,6 +31,8 @@
 //
 // For information about setting deadlines, reusing contexts, and more
 // please visit godoc.org/cloud.google.com/go.
+//
+// Deprecated. This package will be removed in a later release.
 package expr // import "cloud.google.com/go/expr/apiv1alpha1"
 
 import (
diff --git a/internal/gapicgen/generator/config.go b/internal/gapicgen/generator/config.go
index ccd18a4..ac34769 100644
--- a/internal/gapicgen/generator/config.go
+++ b/internal/gapicgen/generator/config.go
@@ -572,6 +572,7 @@
 		gRPCServiceConfigPath: "google/api/expr/v1alpha1/cel_grpc_service_config.json",
 		apiServiceConfigPath:  "google/api/expr/v1alpha1/cel.yaml",
 		releaseLevel:          "alpha",
+		stopGeneration:        true,
 	},
 	{
 		inputDirectoryPath:    "google/devtools/containeranalysis/v1beta1",