[Kernel] Use tables for export groups.

src/xenia/kernel/xam/xam_user.cc

@@ -788,5 +788,4 @@ DECLARE_XAM_EXPORT1(XamSessionRefObjByHandle, kUserProfiles, kStub);
 }  // namespace kernel
 }  // namespace xe
 
-void xe::kernel::xam::RegisterUserExports(
-    xe::cpu::ExportResolver* export_resolver, KernelState* kernel_state) {}
+DECLARE_XAM_EMPTY_REGISTER_EXPORTS(User);