[Security] removed obsolete comment
[Security] Fixed problem with losing ROLE_PREVIOUS_ADMIN role.
bug #8997 [Security] Fixed problem with losing ROLE_PREVIOUS_ADMIN role. (pawaclawczyk)

This PR was squashed before being merged into the 2.3 branch (closes #8997).

Discussion
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[Security] Fixed problem with losing ROLE_PREVIOUS_ADMIN role.

<table>
  <tr>
    <td><b>Q</b></td>
    <td><b>A</b></td>
  </tr>
  <tr>
    <td>Bug fix?</td>
    <td>yes</td>
  </tr>
  <tr>
    <td>New feature</td>
    <td>no</td>
  </tr>
  <tr>
    <td>BC breaks?</td>
    <td>no</td>
  </tr>
  <tr>
    <td>Deprecations?</td>
    <td>no</td>
  </tr>
  <tr>
    <td>Tests pass?</td>
    <td>yes</td>
  </tr>
  <tr>
    <td>Fixed tickets</td>
    <td>#3085, #8974</td>
  </tr>
  <tr>
    <td>License</td>
    <td>MIT</td>
  </tr>
  <tr>
    <td>Doc PR</td>
    <td>n/a</td>
  </tr>
</table>

Problem occurs while user is impersonated. Authentication process generates new token and doeas not preserve role ```ROLE_PREVIOUS_ADMIN```. Ex. when parameter ```security.always_authenticate_before_granting``` is enabled.

Commits
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a7baa3b [Security] Fixed problem with losing ROLE_PREVIOUS_ADMIN role.
Merge branch '2.3' into 2.4

* 2.3:
  fix some cs
  use restore_error_handler instead of set_error_handler($previous)
  fix #9321 Crawler::addHtmlContent add gbk encoding support
  [Console] fixed column width when using the Table helper with some decoration in cells
  [Security] Fixed problem with losing ROLE_PREVIOUS_ADMIN role.
  Fix for cache-key conflict when having a \Traversable as choices
  [Security] removed obsolete comment

Conflicts:
	src/Symfony/Component/Console/Helper/TableHelper.php
	src/Symfony/Component/Security/Tests/Http/Firewall/ExceptionListenerTest.php