Apply modernize-use-equals-default

test/device/_config.cxx

@@ -91,8 +91,7 @@ class TestDevice : public FairMQDevice
 class Config : public ::testing::Test
 {
   public:
-    Config()
-    {}
+    Config() = default;
 
     string TestDeviceSetConfig(const string& transport)
     {

test/device/_transitions.cxx

@@ -23,7 +23,7 @@ using namespace fair::mq;
 class SlowDevice : public FairMQDevice
 {
   public:
-    SlowDevice() {}
+    SlowDevice() = default;
 
   protected:
     void Init()

test/plugin_services/_config.cxx

@@ -13,10 +13,10 @@
 
 struct MyClass
 {
-    MyClass() {}
+    MyClass() = default;
     MyClass(const std::string& a) : msg(a) {}
     MyClass(const MyClass&) = default;
-    MyClass& operator=(const MyClass& b) { msg = b.msg; return *this; };
+    MyClass& operator=(const MyClass& b) = default;
     std::string msg;
 };