Remove legacy hydration mode (#28440)

While Meta is still using legacy mode and we can't remove completely,
Meta is not using legacy hydration so we should be able to remove that.

This is just the first step. Once removed, we can vastly simplify the
DOMConfig for hydration.

This will have to be rebased when tests are upgraded.

DiffTrain build for commit 670d61b.

Author: sebmarkbage

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-dev.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<21dac50eb838d3086d9a7abc82a7da35>>
+ * @generated SignedSource<<3512f830a7f7738685a3f378f1fc8206>>
  */
 
 "use strict";
@@ -14614,15 +14614,6 @@ if (__DEV__) {
         // This is the first render pass. Attempt to hydrate.
         pushPrimaryTreeSuspenseHandler(workInProgress); // We should never be hydrating at this point because it is the first pass,
 
-        if ((workInProgress.mode & ConcurrentMode) === NoMode) {
-          return retrySuspenseComponentWithoutHydrating(
-            current,
-            workInProgress,
-            renderLanes,
-            null
-          );
-        }
-
         if (isSuspenseInstanceFallback()) {
           // This boundary is in a permanent fallback state. In this case, we'll never
           // get an update and we'll never be able to hydrate the final content. Let's just try the
@@ -25519,7 +25510,7 @@ if (__DEV__) {
       return root;
     }
 
-    var ReactVersion = "19.0.0-canary-d06a69d2";
+    var ReactVersion = "19.0.0-canary-ce2d02ca";
 
     // Might add PROFILE later.