[ledger] Switch from InterfacePtr::Close(zx_status_t) to Unbind()

Close(zx_status_t) is being removed since epitaphs are only meant to be
sent from server to client.

Test: fx run-test ledger_unittests
Change-Id: Ide3dbd2e1420e7b1b625c40d71acc54d5160caa3
diff --git a/bin/ledger/fidl/error_notifier/error_notifier_binding_unittest.cc b/bin/ledger/fidl/error_notifier/error_notifier_binding_unittest.cc
index 7084e42..5355bfc 100644
--- a/bin/ledger/fidl/error_notifier/error_notifier_binding_unittest.cc
+++ b/bin/ledger/fidl/error_notifier/error_notifier_binding_unittest.cc
@@ -268,7 +268,7 @@
   binding_.set_on_empty(callback::SetWhenCalled(&called));
   RunLoopUntilIdle();
   EXPECT_FALSE(called);
-  ptr_.Close(ZX_OK);
+  ptr_.Unbind();
   RunLoopUntilIdle();
   EXPECT_TRUE(called);
 }
@@ -280,7 +280,7 @@
   ptr_->NoResponse();
   RunLoopUntilIdle();
   EXPECT_FALSE(called);
-  ptr_.Close(ZX_OK);
+  ptr_.Unbind();
   RunLoopUntilIdle();
   EXPECT_FALSE(called);
   impl_.RunDelayedCallback();