Make wxMBConv dtor inline

The Darwin linking problem mentioned in the comment doesn't exist in any
of the still supported macOS versions, so it doesn't make sense to
continue working around it.

include/wx/strconv.h

@@ -160,7 +160,7 @@ public:
     virtual wxMBConv *Clone() const = 0;
 
     // virtual dtor for any base class
-    virtual ~wxMBConv();
+    virtual ~wxMBConv() { }
 };
 
 // ----------------------------------------------------------------------------

src/common/strconv.cpp

@@ -394,11 +394,6 @@ size_t wxMBConv::WC2MB(char *outBuff, const wchar_t *inBuff, size_t outLen) cons
     return rc;
 }
 
-wxMBConv::~wxMBConv()
-{
-    // nothing to do here (necessary for Darwin linking probably)
-}
-
 wxWCharBuffer wxMBConv::cMB2WC(const char *psz) const
 {
     if ( psz )