Remove obsolete Darwin-specific code in dynlib.*/dlunix.cpp

We don't have our own dlxxx() implementations under Darwin since 76c5594
(Remove our own dlxxx() functions emulation for OS X <= 10.3.,
2013-10-17).

wxHAVE_DYNLIB_ERROR is reduced to being the same HAVE_DLERROR, so use
the latter one instead.

Closes https://github.com/wxWidgets/wxWidgets/pull/1826

include/wx/dynlib.h

@@ -18,11 +18,6 @@
 #include "wx/string.h"
 #include "wx/dynarray.h"
 
-// note that we have our own dlerror() implementation under Darwin
-#if defined(HAVE_DLERROR) || defined(__DARWIN__)
-    #define wxHAVE_DYNLIB_ERROR
-#endif
-
 class WXDLLIMPEXP_FWD_BASE wxDynamicLibraryDetailsCreator;
 
 // ----------------------------------------------------------------------------
@@ -31,9 +26,6 @@ class WXDLLIMPEXP_FWD_BASE wxDynamicLibraryDetailsCreator;
 
 #if defined(__WINDOWS__)
     typedef WXHMODULE           wxDllType;
-#elif defined(__DARWIN__)
-    // Don't include dlfcn.h on Darwin, we may be using our own replacements.
-    typedef void               *wxDllType;
 #elif defined(HAVE_DLOPEN)
     #include <dlfcn.h>
     typedef void               *wxDllType;
@@ -365,10 +357,10 @@ protected:
     // common part of GetSymbol() and HasSymbol()
     void* DoGetSymbol(const wxString& name, bool* success = NULL) const;
 
-#ifdef wxHAVE_DYNLIB_ERROR
+#ifdef HAVE_DLERROR
     // log the error after a dlxxx() function failure
     static void Error();
-#endif // wxHAVE_DYNLIB_ERROR
+#endif // HAVE_DLERROR
 
 
     // the handle to DLL or NULL