Cocoa: Remove checks for pre-10.8 SDK

OS X 10.8 is now the minimum required version but these checks were not
removed when that change was made.

src/cocoa_init.m

@@ -435,13 +435,9 @@ static GLFWbool initializeTIS(void)
 
         if ([[NSBundle mainBundle] pathForResource:@"MainMenu" ofType:@"nib"])
         {
-#if MAC_OS_X_VERSION_MAX_ALLOWED >= 1080
             [[NSBundle mainBundle] loadNibNamed:@"MainMenu"
                                           owner:NSApp
                                 topLevelObjects:&_glfw.ns.nibObjects];
-#else
-            [[NSBundle mainBundle] loadNibNamed:@"MainMenu" owner:NSApp];
-#endif
         }
         else
             createMenuBar();