[Fizz] Stop publishing external-runtime to stable channel (#28796)

The external runtime is not vetted for stability yet. We should stop
publishing it with our stable build

packages/shared/ReactFeatureFlags.js

@@ -110,7 +110,7 @@ export const enableUseEffectEventHook = __EXPERIMENTAL__;
 // Test in www before enabling in open source.
 // Enables DOM-server to stream its instruction set as data-attributes
 // (handled with an MutationObserver) instead of inline-scripts
-export const enableFizzExternalRuntime = true;
+export const enableFizzExternalRuntime = __EXPERIMENTAL__;
 
 export const alwaysThrottleRetries = true;
 

scripts/rollup/bundles.js

@@ -328,7 +328,7 @@ const bundles = [
 
   /******* React DOM Fizz Server External Runtime *******/
   {
-    bundleTypes: [BROWSER_SCRIPT],
+    bundleTypes: __EXPERIMENTAL__ ? [BROWSER_SCRIPT] : [],
     moduleType: RENDERER,
     entry: 'react-dom/unstable_server-external-runtime',
     outputPath: 'unstable_server-external-runtime.js',

scripts/rollup/packaging.js

@@ -235,7 +235,14 @@ function filterOutEntrypoints(name) {
       // Let's remove it.
       files.splice(i, 1);
       i--;
-      unlinkSync(`build/node_modules/${name}/${filename}`);
+      try {
+        unlinkSync(`build/node_modules/${name}/${filename}`);
+      } catch (err) {
+        // If the file doesn't exist we can just move on. Otherwise throw the halt the build
+        if (err.code !== 'ENOENT') {
+          throw err;
+        }
+      }
       changed = true;
       // Remove it from the exports field too if it exists.
       if (exportsJSON) {