[cleanup] Remove redundant forward declaration of tiering-manager.h

Parameter of class UnoptimizedFrame and JavaScriptFrame was removed.

Change-Id: I37c43ff491f039820f40d60ed9ada43fd59e7c05
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3725613Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Tao Pan <tao.pan@intel.com>
Cr-Commit-Position: refs/heads/main@{#81398}

src/execution/tiering-manager.h

@@ -14,8 +14,6 @@ namespace internal {
 
 class BytecodeArray;
 class Isolate;
-class UnoptimizedFrame;
-class JavaScriptFrame;
 class JSFunction;
 class OptimizationDecision;
 enum class CodeKind : uint8_t;