Get rid of compile- and run-time checks for OS X < 10.5.

As 10.5 is the minimal supported version, it doesn't make sense to check for
it (or even earlier versions) during the build or run-time.

Closes #15580.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75028 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/cocoa/private.h

@@ -19,12 +19,6 @@
     #import <Cocoa/Cocoa.h>
 #endif
 
-#if MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_5
-// available in 10.4 but not in the headers
-enum {
-    kEventMouseScroll             = 11
-};
-#endif
 //
 // shared between Cocoa and Carbon
 //