Hide the "safe browsing" settings

Decided below to just hide the entire section.

Original issue description:

After the rebase on 149, the settings now show a warning that may encourage users to switch "Block dangerous and deceptive content", which would be non-default for Tor Browser.

Screenshot of the settings for "Deceptive content and dangerous software protection".

I don't know much about this feature, or why we have decided to keep these settings visible. @morgan @pierov or @ma1 do you know the background?

In any case, the warning banner is encouraging users to switch, so I imagine we want to hide this.

/cc @donuts @felicia

Edited by henry