Put the gpt header and footer in the assembly dir

These are not instance-specific.

Test: Build and run locally, check ~/cuttlefish_assembly
Bug: 145247175
Change-Id: I07332b79e44491eddbb91f283856a0c9c6accee9
diff --git a/host/commands/assemble_cvd/flags.cc b/host/commands/assemble_cvd/flags.cc
index ff91c8e..39db389 100644
--- a/host/commands/assemble_cvd/flags.cc
+++ b/host/commands/assemble_cvd/flags.cc
@@ -574,9 +574,8 @@
     LOG(FATAL) << "asked to create composite disk, but path was empty";
   }
   if (FLAGS_vm_manager == vm_manager::CrosvmManager::name()) {
-    auto instance = config.ForDefaultInstance();
-    std::string header_path = instance.PerInstancePath("gpt_header.img");
-    std::string footer_path = instance.PerInstancePath("gpt_footer.img");
+    std::string header_path = config.AssemblyPath("gpt_header.img");
+    std::string footer_path = config.AssemblyPath("gpt_footer.img");
     create_composite_disk(disk_config(), header_path, footer_path, FLAGS_composite_disk);
   } else {
     aggregate_image(disk_config(), FLAGS_composite_disk);