Release process: drop unnecessary encryption requirement

Anyone can gather by themselves the info we're sharing here,
and the subsequent mirror pool changes will be public anyway,
so I don't see why we would explicitly require encryption here.

wiki/src/contribute/release_process.mdwn

@@ -1590,7 +1590,7 @@ Make sure every active mirror in the pool has the new version:
 
 Ask the mirrors team to disable mirrors that are lagging behind:
 
- - either over email: <tails-mirrors@boum.org> [encrypted]
+ - either over email: <tails-mirrors@boum.org>
  - or by creating a merge request that modifies the
    [mirrors configuration file](https://gitlab.tails.boum.org/tails/mirror-pool/-/blob/master/mirrors.json)