Delete Inky Email Templating Language documentation

The Inky framework has not been actively developed for about three years (last release in March 2022). In addition to Sass deprecations and other bugs, the project is generally no longer up to date when it comes to implementing email templates.

In my opinion, it no longer makes sense to list the project as the only solution for designed emails.

Author: FlorianBoe

mailer.rst

@@ -1255,62 +1255,6 @@ the entire email contents from Markdown to HTML:
         [Activate your account]({{ url('...') }})
     {% endapply %}
 
-.. _mailer-inky:
-
-Inky Email Templating Language
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Creating beautifully designed emails that work on every email client is so
-complex that there are HTML/CSS frameworks dedicated to that. One of the most
-popular frameworks is called `Inky`_. It defines a syntax based on some HTML-like
-tags which are later transformed into the real HTML code sent to users:
-
-.. code-block:: html
-
-    <!-- a simplified example of the Inky syntax -->
-    <container>
-        <row>
-            <columns>This is a column.</columns>
-        </row>
-    </container>
-
-Twig provides integration with Inky via the ``InkyExtension``. First, install
-the extension in your application:
-
-.. code-block:: terminal
-
-    $ composer require twig/extra-bundle twig/inky-extra
-
-The extension adds an ``inky_to_html`` filter, which can be used to convert
-parts or the entire email contents from Inky to HTML:
-
-.. code-block:: html+twig
-
-    {% apply inky_to_html %}
-        <container>
-            <row class="header">
-                <columns>
-                    <spacer size="16"></spacer>
-                    <h1 class="text-center">Welcome {{ email.toName }}!</h1>
-                </columns>
-
-                {# ... #}
-            </row>
-        </container>
-    {% endapply %}
-
-You can combine all filters to create complex email messages:
-
-.. code-block:: twig
-
-    {% apply inky_to_html|inline_css(source('@styles/foundation-emails.css')) %}
-        {# ... #}
-    {% endapply %}
-
-This makes use of the :ref:`styles Twig namespace <mailer-css-namespace>` we created
-earlier. You could, for example, `download the foundation-emails.css file`_
-directly from GitHub and save it in ``assets/styles``.
-
 .. _signing-and-encrypting-messages:
 
 Signing and Encrypting Messages
@@ -2279,7 +2223,6 @@ the :class:`Symfony\\Bundle\\FrameworkBundle\\Test\\MailerAssertionsTrait`::
 .. _`Google Gmail`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Mailer/Bridge/Google/README.md
 .. _`high availability`: https://en.wikipedia.org/wiki/High_availability
 .. _`Infobip`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Mailer/Bridge/Infobip/README.md
-.. _`Inky`: https://get.foundation/emails/docs/inky.html
 .. _`league/html-to-markdown`: https://github.com/thephpleague/html-to-markdown
 .. _`load balancing`: https://en.wikipedia.org/wiki/Load_balancing_(computing)
 .. _`MailerSend`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Mailer/Bridge/MailerSend/README.md