LibJS: Use Function as callback type in define_native_function/accessor

There is not need to use SafeFunction because
define_native_function or define_native_accessor will pass callback
forward to NativeFunction that uses HeapFunction to visit it.

Userland/Libraries/LibJS/Runtime/Object.cpp

@@ -1197,7 +1197,7 @@ void Object::set_prototype(Object* new_prototype)
         m_shape = shape.create_prototype_transition(new_prototype);
 }
 
-void Object::define_native_accessor(Realm& realm, PropertyKey const& property_key, SafeFunction<ThrowCompletionOr<Value>(VM&)> getter, SafeFunction<ThrowCompletionOr<Value>(VM&)> setter, PropertyAttributes attribute)
+void Object::define_native_accessor(Realm& realm, PropertyKey const& property_key, Function<ThrowCompletionOr<Value>(VM&)> getter, Function<ThrowCompletionOr<Value>(VM&)> setter, PropertyAttributes attribute)
 {
     FunctionObject* getter_function = nullptr;
     if (getter)
@@ -1257,7 +1257,7 @@ Value Object::get_without_side_effects(PropertyKey const& property_key) const
     return {};
 }
 
-void Object::define_native_function(Realm& realm, PropertyKey const& property_key, SafeFunction<ThrowCompletionOr<Value>(VM&)> native_function, i32 length, PropertyAttributes attribute)
+void Object::define_native_function(Realm& realm, PropertyKey const& property_key, Function<ThrowCompletionOr<Value>(VM&)> native_function, i32 length, PropertyAttributes attribute)
 {
     auto function = NativeFunction::create(realm, move(native_function), length, property_key, &realm);
     define_direct_property(property_key, function, attribute);

Userland/Libraries/LibJS/Runtime/Object.h

@@ -166,8 +166,8 @@ public:
     using IntrinsicAccessor = Value (*)(Realm&);
     void define_intrinsic_accessor(PropertyKey const&, PropertyAttributes attributes, IntrinsicAccessor accessor);
 
-    void define_native_function(Realm&, PropertyKey const&, SafeFunction<ThrowCompletionOr<Value>(VM&)>, i32 length, PropertyAttributes attributes);
-    void define_native_accessor(Realm&, PropertyKey const&, SafeFunction<ThrowCompletionOr<Value>(VM&)> getter, SafeFunction<ThrowCompletionOr<Value>(VM&)> setter, PropertyAttributes attributes);
+    void define_native_function(Realm&, PropertyKey const&, Function<ThrowCompletionOr<Value>(VM&)>, i32 length, PropertyAttributes attributes);
+    void define_native_accessor(Realm&, PropertyKey const&, Function<ThrowCompletionOr<Value>(VM&)> getter, Function<ThrowCompletionOr<Value>(VM&)> setter, PropertyAttributes attributes);
 
     virtual bool is_dom_node() const { return false; }
     virtual bool is_function() const { return false; }