minor #16124 [Frontend] Remove all Assetic references (javiereguiluz)

This PR was merged into the 6.0 branch.

Discussion
----------

[Frontend] Remove all Assetic references

We kept this placeholder article for some time, because some projects were still using Assetic. However, nowadays this is completely legacy, so I propose to remove it in 6.0 branch.

Commits
-------

5d033cf [Frontend] Remove all Assetic references

Author: javiereguiluz

_build/redirection_map

@@ -534,3 +534,5 @@
 /security/multiple_guard_authenticators /security/entry_point
 /security/guard_authentication /security/custom_authenticator
 /email /mailer
+/frontend/assetic /frontend
+/frontend/assetic/index /frontend

_build/spelling_word_list.txt

@@ -3,7 +3,6 @@ Akamai
 analytics
 Ansi
 Ansible
-Assetic
 async
 authenticator
 authenticators

frontend.rst

@@ -92,7 +92,6 @@ Other Front-End Articles
     :hidden:
     :glob:
 
-    frontend/assetic/index
     frontend/encore/installation
     frontend/encore/simple-example
     frontend/encore/*