cap_msmf.hpp: fix a warning about nNull being unused

The two functions featuring nNull are not particularly needed, so
I simply removed them.

Conflicts:
	modules/highgui/src/cap_msmf.hpp

modules/videoio/src/cap_msmf.hpp

@@ -603,11 +603,6 @@ public:
     ComPtr() throw()
     {
     }
-    ComPtr(int nNull) throw()
-    {
-        assert(nNull == 0);
-        p = NULL;
-    }
     ComPtr(T* lp) throw()
     {
         p = lp;
@@ -638,13 +633,6 @@ public:
     {
         return p.operator==(pT);
     }
-    // For comparison to NULL
-    bool operator==(int nNull) const
-    {
-        assert(nNull == 0);
-        return p.operator==(NULL);
-    }
-
     bool operator!=(_In_opt_ T* pT) const throw()
     {
         return p.operator!=(pT);
@@ -3123,7 +3111,7 @@ public:
         HRESULT hr = CheckShutdown();
 
         if (SUCCEEDED(hr)) {
-            if (m_spClock == NULL) {
+            if (!m_spClock) {
                 hr = MF_E_NO_CLOCK; // There is no presentation clock.
             } else {
                 // Return the pointer to the caller.