remove `gc_on_delete`

include/pocketpy/interpreter/heap.h

@@ -9,8 +9,6 @@ typedef struct ManagedHeap{
     bool gc_enabled;
     
     VM* vm;
-
-    void (*gc_on_delete)(VM*, PyObject*);
 } ManagedHeap;
 
 void ManagedHeap__ctor(ManagedHeap* self, VM* vm);

src/interpreter/heap.c

@@ -12,8 +12,6 @@ void ManagedHeap__ctor(ManagedHeap* self, VM* vm) {
     self->gc_enabled = true;
 
     self->vm = vm;
-
-    self->gc_on_delete = NULL;
 }
 
 void ManagedHeap__dtor(ManagedHeap* self) {
@@ -55,7 +53,6 @@ int ManagedHeap__sweep(ManagedHeap* self) {
             obj->gc_marked = false;
             c11_vector__push(PyObject*, &alive, obj);
         } else {
-            if(self->gc_on_delete) { self->gc_on_delete(self->vm, obj); }
             PyObject__delete(obj);
         }
     }