Remove @check_tor_leaks tag and always look for leaks

The reason I made the Tor check opt-in via the @check_tor_leaks was that I envisioned it later turning in to a @uses_tor tag, that also would deal with scenario re-running on failure and other stuff. It seems clear now that won’t ever happen (instead we seem to go the #9519 way), so I think we should just always run this both to simplify our .feature files, and to make sure we never forget this for new scenarios.

We’ll need a way to opt-out from this though: some scenarios, such as “The Unsafe Browser can load a web page”, are expected to generate non-Tor traffic.

Parent Task: #10237

Original created by @anonym on 11376 (Redmine)