Remove stale task/comment in FabricUIManager (#40768)

Summary:
Pull Request resolved: #40768

The task referenced is 4 years old and it doesn't seem to be relevant anymore given that:
* `addRootView` has been marked as deprecated
* there is an explicit check in `addRootView` mentioning:

> Do not call addRootView in Fabric; it is unsupported. Call startSurface instead

Changelog: [Internal]

Reviewed By: sammy-SC

Differential Revision: D50122192

fbshipit-source-id: fe02d481b47663f5bdf4fb7527e480117f00be47

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManager.java

@@ -232,7 +232,6 @@ public FabricUIManager(
     mReactApplicationContext.registerComponentCallbacks(viewManagerRegistry);
   }
 
-  // TODO (T47819352): Rename this to startSurface for consistency with xplat/iOS
   @Override
   @UiThread
   @ThreadConfined(UI)