heap: Fix monolith build

Fix monolith build complaning about used implicit copy ctor when copy
operator is explicitly defined.

Bug: v8:12402
Change-Id: Iec30882af1c825c277a2e538400c85348daa6301
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3289624
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77951}

src/heap/heap.cc

@@ -194,9 +194,6 @@ bool Heap::GCCallbackTuple::operator==(
   return other.callback == callback && other.data == data;
 }
 
-Heap::GCCallbackTuple& Heap::GCCallbackTuple::operator=(
-    const Heap::GCCallbackTuple& other) V8_NOEXCEPT = default;
-
 class ScavengeTaskObserver : public AllocationObserver {
  public:
   ScavengeTaskObserver(Heap* heap, intptr_t step_size)

src/heap/heap.h

@@ -1725,7 +1725,6 @@ class Heap {
         : callback(callback), gc_type(gc_type), data(data) {}
 
     bool operator==(const GCCallbackTuple& other) const;
-    GCCallbackTuple& operator=(const GCCallbackTuple& other) V8_NOEXCEPT;
 
     v8::Isolate::GCCallbackWithData callback;
     GCType gc_type;