refactor: remove dead types of fiber (#28405)

The properties `firstEffect` and `lastEffect` of the Fiber are currently
not being used and are considered to be dead code, and can be removed.

Author: bubucuo

packages/react-reconciler/src/ReactInternalTypes.js

@@ -157,12 +157,6 @@ export type Fiber = {
   subtreeFlags: Flags,
   deletions: Array<Fiber> | null,
 
-  // The first and last fiber with side-effect within this subtree. This allows
-  // us to reuse a slice of the linked list when we reuse the work done within
-  // this fiber.
-  firstEffect: Fiber | null,
-  lastEffect: Fiber | null,
-
   lanes: Lanes,
   childLanes: Lanes,