Hide the history related UI when in private browsing mode

From: #44001 (comment 3246162)

There are many ways to access the history, even though it's disabled.

We should consider disabling this UI in those cases.

From the linked note:

From what I gather, you can access history in many ways:

1. From the search bar, by typing @history as is mentioned here.
2. From the top right hamburger menu, by going to the "History" item.
3. By typing Ctrl + H, which opens the history sidebar. (History sidebar only works when using the old sidebar, by the way. In vertical tabs mode, it is a blank -- see #44108).
4. From the top menu, by typing e.g. Alt+Shfit+B and opening the "History" dropdown.
5. From the old sidebar i.e. not the new tabs sidebar, so you have to pick "Horizontal tabs" and uncheck "Show sidebar" in settings under "Browser Layout". You can access it by clicking on the header of the sidebar and choosing "History".
6. I would not be surpirsed if there are more ways to access it.