minor #19973 remove Silex mention in favor of Symfony (94noni)

This PR was submitted for the 7.1 branch but it was merged into the 5.4 branch instead.

Discussion
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remove Silex mention in favor of Symfony

Commits
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754f12d Update http_kernel.rst

Author: javiereguiluz

components/http_kernel.rst

@@ -3,8 +3,8 @@ The HttpKernel Component
 
     The HttpKernel component provides a structured process for converting
     a ``Request`` into a ``Response`` by making use of the EventDispatcher
-    component. It's flexible enough to create a full-stack framework (Symfony),
-    a micro-framework (Silex) or an advanced CMS system (Drupal).
+    component. It's flexible enough to create a full-stack framework (Symfony)
+    or an advanced CMS (Drupal).
 
 Installation
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