Revert "rpc: fix erroneous error-message in test (ethereum#28227)"

This reverts commit 22de582.

rpc/server_test.go

@@ -32,18 +32,17 @@ func TestServerRegisterName(t *testing.T) {
 	server := NewServer()
 	service := new(testService)
 
-	svcName := "test"
-	if err := server.RegisterName(svcName, service); err != nil {
+	if err := server.RegisterName("test", service); err != nil {
 		t.Fatalf("%v", err)
 	}
 
 	if len(server.services.services) != 2 {
 		t.Fatalf("Expected 2 service entries, got %d", len(server.services.services))
 	}
 
-	svc, ok := server.services.services[svcName]
+	svc, ok := server.services.services["test"]
 	if !ok {
-		t.Fatalf("Expected service %s to be registered", svcName)
+		t.Fatalf("Expected service calc to be registered")
 	}
 
 	wantCallbacks := 14