minor #17143 [Config] Delete a page that it's no longer needed (javiereguiluz)

This PR was squashed before being merged into the 4.4 branch.

Discussion
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[Config] Delete a page that it's no longer needed

Fixes #17133.

Symfony 4.4, the oldest maintained Symfony version, was released on November 2019, so this page is no longer relevant.

When we delete or move some doc page, we always provide an alternative to avoid errors. In this case, this page is so special that it doesn't really have an alternative. Redirecting to any other page would be wrong. So, let's delete the file and people visiting the page will see an error page showing that the page is only available for some past Symfony versions.

Commits
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4150590 [Config] Delete a page that it's no longer needed

Author: javiereguiluz

configuration.rst

@@ -687,12 +687,6 @@ the env files ending in ``.local`` (``.env.local`` and ``.env.<environment>.loca
 **should not be committed** because only you will use them. In fact, the
 ``.gitignore`` file that comes with Symfony prevents them from being committed.
 
-.. caution::
-
-    Applications created before November 2018 had a slightly different system,
-    involving a ``.env.dist`` file. For information about upgrading, see:
-    :doc:`configuration/dot-env-changes`.
-
 .. _configuration-env-var-in-prod:
 
 Configuring Environment Variables in Production