Revert "Unwrap sync resolved thenables without suspending (facebook#25615)"

This reverts commit 1a90262.

If a thenable resolves synchronously, `use` should unwrap its result
without suspending or interrupting the component's execution.

Author: acdlite

packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js

@@ -5426,33 +5426,6 @@ describe('ReactDOMFizzServer', () => {
       expect(Scheduler).toFlushAndYield([]);
       expect(getVisibleChildren(container)).toEqual('Hi');
     });
-
-    // @gate enableUseHook
-    it('unwraps thenable that fulfills synchronously without suspending', async () => {
-      function App() {
-        const thenable = {
-          then(resolve) {
-            // This thenable immediately resolves, synchronously, without waiting
-            // a microtask.
-            resolve('Hi');
-          },
-        };
-        try {
-          return <Text text={use(thenable)} />;
-        } catch {
-          throw new Error(
-            '`use` should not suspend because the thenable resolved synchronously.',
-          );
-        }
-      }
-      // Because the thenable resolves synchronously, we should be able to finish
-      // rendering synchronously, with no fallback.
-      await act(async () => {
-        const {pipe} = renderToPipeableStream(<App />);
-        pipe(writable);
-      });
-      expect(getVisibleChildren(container)).toEqual('Hi');
-    });
   });
 
   describe('useEvent', () => {

packages/react-server/src/ReactFizzThenable.js

@@ -83,36 +83,24 @@ export function trackUsedThenable<T>(
         // it's defined, but an unknown value, assume it's been instrumented by
         // some custom userspace implementation. We treat it as "pending".
       } else {
-        const pendingThenable: PendingThenable<T> = (thenable: any);
+        const pendingThenable: PendingThenable<mixed> = (thenable: any);
         pendingThenable.status = 'pending';
         pendingThenable.then(
           fulfilledValue => {
             if (thenable.status === 'pending') {
-              const fulfilledThenable: FulfilledThenable<T> = (thenable: any);
+              const fulfilledThenable: FulfilledThenable<mixed> = (thenable: any);
               fulfilledThenable.status = 'fulfilled';
               fulfilledThenable.value = fulfilledValue;
             }
           },
           (error: mixed) => {
             if (thenable.status === 'pending') {
-              const rejectedThenable: RejectedThenable<T> = (thenable: any);
+              const rejectedThenable: RejectedThenable<mixed> = (thenable: any);
               rejectedThenable.status = 'rejected';
               rejectedThenable.reason = error;
             }
           },
         );
-
-        // Check one more time in case the thenable resolved synchronously
-        switch (thenable.status) {
-          case 'fulfilled': {
-            const fulfilledThenable: FulfilledThenable<T> = (thenable: any);
-            return fulfilledThenable.value;
-          }
-          case 'rejected': {
-            const rejectedThenable: RejectedThenable<T> = (thenable: any);
-            throw rejectedThenable.reason;
-          }
-        }
       }
 
       // Suspend.