Hide the History section in `about:preferences#privacy`

May also be applicable to Tor Browser.

Since we don't support non PBM and changing that has an effect on the design/threat model of the browser, why do we keep exposing the UI to change it?

I suggest we hide it as to not encourage users to change anything. If they feel like they know better, they can change stuff in about:config.

Visual interpretation:

(and no, I'm not suggesting drawing a red cross on top it @ma1 ;) )

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