Update URL bar onion indicators

Since FF70, the green locks at the URL bar are gone. The current Firefox approach to security indicators is detailed here[1]. Chrome is leading towards this intention, too[2].

As part of S27, I'm working on unifying (and simplifying) the brand presence of onions in Tor Browser, either for referring to the network or to the onion services.

I'm opening this ticket to discuss the following:

• are we ok following the Firefox approach and removing green icons from the URL bar?
• are we ok unifying the visual anchor for onions and onion routing at the URL bar and also at the circuit display?
• are we ok removing EV label from the URL bar and leave it at the identity doorhanger?

[1]FF70 https://blog.mozilla.org/security/2019/10/15/improved-security-and-privacy-indicators-in-firefox-70/ [2]CH69 https://blog.chromium.org/2018/05/evolving-chromes-security-indicators.html [*]TB8 https://trac.torproject.org/projects/tor/wiki/org/teams/UxTeam/Misc/OnionSecurityIndicator