tidy: Replace default special member functions with the =default keyw…

…ord.

Clang-tidy pointed out one places where a structure destructor was
identical to what the compiler would generate.  Marking this function
as "=default" allows the compiler more optimization chances.

This code was pointed out by clang-tidy's "use =default" check.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-equals-default.html

mythtv/libs/libmythbase/mythpower.cpp

@@ -123,10 +123,6 @@ MythPower::MythPower()
     connect(&m_featureTimer, &QTimer::timeout, this, &MythPower::FeatureTimeout);
 }
 
-MythPower::~MythPower()
-{
-}
-
 void MythPower::Init(void)
 {
     QStringList supported;

mythtv/libs/libmythbase/mythpower.h

@@ -74,7 +74,7 @@ class MBASE_PUBLIC MythPower : public QObject, public ReferenceCounter
     static QMutex s_lock;
 
     MythPower();
-    virtual ~MythPower();
+    virtual ~MythPower() = default;
 
     virtual void   Init              (void);
     virtual bool   DoFeature         (bool = false) { return false; }

mythtv/libs/libmythui/platforms/mythdisplayx11.cpp

@@ -21,10 +21,6 @@ MythDisplayX11::MythDisplayX11()
     InitialiseModes();
 }
 
-MythDisplayX11::~MythDisplayX11()
-{
-}
-
 bool MythDisplayX11::IsAvailable(void)
 {
     static bool s_checked = false;

mythtv/libs/libmythui/platforms/mythdisplayx11.h

@@ -8,7 +8,7 @@ class MythDisplayX11 : public MythDisplay
 {
   public:
     MythDisplayX11();
-   ~MythDisplayX11() override;
+   ~MythDisplayX11() override = default;
     static bool IsAvailable(void);
     DisplayInfo GetDisplayInfo(int VideoRate = 0) override;