docs: clarify that PHP 7.3 runtime is no longer in beta (GoogleCloudPlatform#1102)

Author: darrencarlton

appengine/php72/helloworld/README.md

@@ -1,6 +1,6 @@
-# Hello World on App Engine Standard for PHP 7.2
+# Hello World on App Engine Standard for PHP 7.2 and 7.3
 
-This sample demonstrates how to deploy a *very* basic application to Google
-App Engine for PHP 7.2.
+This sample demonstrates how to deploy a *very* basic application to the
+PHP 7.2 and 7.3 standard environment in Google App Engine.
 
 ## View the [full tutorial](https://cloud.google.com/appengine/docs/standard/php7/quickstart)

appengine/php72/helloworld/app.yaml

@@ -1,4 +1,4 @@
-# Use the PHP 7.3 runtime (BETA) by replacing "php72" below with "php73"
+# Use PHP 7.3 by replacing "php72" below with "php73"
 runtime: php72
 
 # Defaults to "serve index.php" and "serve public/index.php". Can be used to