Fix buffer_fill test, rework new node operator= checks

Author: Bensuo

sycl/test-e2e/Graph/Inputs/buffer_fill.cpp

@@ -14,8 +14,7 @@ int main() {
     exp_ext::command_graph Graph{
         Queue.get_context(),
         Queue.get_device(),
-        {exp_ext::property::graph::assume_buffer_outlives_graph{},
-         exp_ext::property::graph::assume_data_outlives_buffer{}}};
+        {exp_ext::property::graph::assume_buffer_outlives_graph{}}};
 
     auto NodeA = add_node(Graph, Queue, [&](handler &CGH) {
       auto Acc = Buffer.get_access(CGH);