Safari 9: Can't disable private browsing

Hi there! I really need some help. I wanted to remove private browsing on my Safari 9, and I have found a lot of posts, websites and threads on how to remove private browsing, and mainly, this is what I found:

1. Go to applications folder in Finder

2. 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 a respective folder for whatever language you have maybe)

4. Double click on MainMenu.nib to open it in interface builder

5. 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 and it disappears!

7. hit command+s to save, close interface builder if you want, and relaunch safari.

So, I followed the steps up to the 4th, whereas I noticed that MainMenu.nib doesn't exist in my English.lproj. So, with that, I couldn't do anything. I tried opening the other MainMenu.nib s for French, German, etc, but all were just pictures and didn't have ACTUAL contents. I really need help with this. I was gonna uninstall Safari, but as I use El Capitan I couldn't, which I then noticed that on El Capitan you can't delete Safari. Please do help me.

[SIDE NOTE] The most reason why I want to disable private browsing is because of any form of explicit results that is unsuitable for certain ages. So what came across my mind is enabling SafeSearch for Private Browsing, but since when you close a private window all the cookies are removed, the SafeSearch option doesn't save (in which I wanted it to). Based on this thread by Google: https://productforums.google.com/forum/#!topic/websearch/mJ-BUVoLA08

It indicates that I can use SafeSearch on private windows if I enable third-party cookies. I couldn't figure out how to do so, so if you can't solve the first question, please do help me with this one if you can.

Any help is appreciated.

Thanks in advance,

- Edward