Remove closed question

wiki/src/blueprint/bootstrapping/extension.mdwn

@@ -220,17 +220,6 @@ mechanism would need to be of the "remote code execution vulnerability"
 and would represent a threat in many more use cases than when verifying
 an ISO image.
 
-Open questions
---------------
-
-As the verification mechanism totally depends on the integrity of web
-pages retrieved from our website and displayed to the user in their
-browser, it would also be vulnerable to an attacker who could manage to
-corrupt the verification mechanism or manipulate what is displayed to
-the user **from inside the browser**. We are [still
-investigating](https://mailman.boum.org/pipermail/tails-dev/2015-April/008648.html)
-whether such attacks are possible.
-
 Checksum verification
 ---------------------