minor symfony#8976 Reworded the setup article about using other versions (javiereguiluz)

This PR was squashed before being merged into the 4.0 branch (closes symfony#8976).

Discussion
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Reworded the setup article about using other versions

  As explained in symfony#8886:

> You can't install specific branch versions with a single command when using Flex, so let's not mention it. The installation of beta and RC versions is covered in other articles, so we're not missing anything by removing this. Thanks!

Commits
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cf97957 Reworded the setup article about using other versions

Author: javiereguiluz

setup.rst

@@ -23,21 +23,6 @@ This will create a new ``my-project`` directory, download some dependencies into
 it and even generate the basic directories and files you'll need to get started.
 In other words, your new app is ready!
 
-.. tip::
-
-    You can also download a specific version of Symfony:
-
-    .. code-block:: terminal
-
-        # use the most recent version in any Symfony branch
-        $ composer create-project symfony/skeleton my-project "4.0.*"
-
-        # use a beta or RC version (useful for testing new Symfony versions)
-        $ composer create-project symfony/skeleton my-project 4.0.0-BETA1
-
-    Some version are long-term support (LTS) versions. Read the :doc:`Symfony Release process </contributing/community/releases>`
-    to learn more.
-
 Running your Symfony Application
 --------------------------------