minor #6068 Remove references to API tagging (dunglas)

This PR was merged into the 2.3 branch.

Discussion
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Remove references to API tagging

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3
| Fixed tickets | n/a

Related to symfony/symfony#15977 and symfony/symfony#15979.

Commits
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d816c7f Remove references to API tagging

Author: xabbuh

contributing/code/_api_tagging.rst.inc

@@ -74,8 +74,6 @@ backwards compatibility promise:
 | Add a default value to an argument            | Yes                         |
 +-----------------------------------------------+-----------------------------+
 
-.. include:: _api_tagging.rst.inc
-
 Using our Classes
 ~~~~~~~~~~~~~~~~~
 
@@ -134,8 +132,6 @@ covered by our backwards compatibility promise:
 | Access a private property (via Reflection)    | No                          |
 +-----------------------------------------------+-----------------------------+
 
-.. include:: _api_tagging.rst.inc
-
 Working on Symfony Code
 -----------------------