Hi and welcome to Just Answer.com a paid global support site. I see you have installed the x code tools that is a great first step as it is necessary to do this. 1. Go to applications folder in Finder2. right click (with a mighty mouse or 2 button mouse, or Control+click for one button mice) on safari and choose "Show Package Contents"3. Go to Contents, then Resources, then English.lproj folder (or for whatever language you have maybe)4. Double click on MainMenu.nib to open it in interface builder5. look at the window with the safari menu, click on Safari to expand it, then click on the Private Browsing menu item.6. hit the delete key 7. hit command+s to save, close interface builder if you want, and relaunch safari.
the trick here is you have to do this every time you update safari