Enable use_once_callback on mojom GN rule by default

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index b2f3540e44a36db4302677b35185870696e97fcf..869ba31c908badeacc8fa4ada22edc4e0291803f 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -463,16 +463,12 @@ mojom("content_test_mojo_bindings") {
     "../public/test/test_service.mojom",
     "test_browser_associated_interfaces.mojom",
   ]
-
-  use_once_callback = true
 }
 
 mojom("web_ui_test_mojo_bindings") {
   sources = [
     "data/web_ui_test_mojo_bindings.mojom",
   ]
-
-  use_once_callback = true
 }
 
 static_library("layouttest_support") {