minor #7247 Revert the merge of #7141 (xabbuh)

This PR was merged into the 2.7 branch.

Discussion
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Revert the merge of #7141

I shouldn't have merged #7141 into the `2.7` branch as the related code PR (symfony/symfony#17532) was released with Symfony 3.1.

Commits
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0f7c7d5 Revert "minor #7141 Added "How to Use a Custom Version Strategy for Assets" (teohhanhui, javiereguiluz)"

Author: xabbuh

frontend/custom_version_strategy.rst

@@ -75,7 +75,6 @@ Configuration
     * `packages`_
     * `version`_
     * `version_format`_
-    * `version_strategy`_
 * `templating`_
     * `hinclude_default_template`_
     * :ref:`form <reference-templating-form>`
@@ -946,8 +945,6 @@ collection each time it generates an asset's path:
             ),
         ));
 
-.. _reference-framework-assets-packages:
-
 packages
 ........
 
@@ -1016,7 +1013,6 @@ Each package can configure the following options:
 * :ref:`base_urls <reference-assets-base-urls>`
 * :ref:`version <reference-framework-assets-version>`
 * :ref:`version_format <reference-assets-version-format>`
-* :ref:`version_strategy <reference-framework-assets-version_strategy>`
 
 .. _reference-framework-assets-version:
 .. _ref-framework-assets-version:
@@ -1094,7 +1090,6 @@ option.
     ``version``. This makes it easier to increment the cache on each
     deployment.
 
-.. _reference-framework-assets-version-format:
 .. _reference-templating-version-format:
 .. _reference-assets-version-format:
 
@@ -1135,16 +1130,6 @@ is set to ``5``, the asset's path would be ``/images/logo.png?version=5``.
     any URL rewriting. The latter option is useful if you would like older
     asset versions to remain accessible at their original URL.
 
-.. _reference-framework-assets-version_strategy:
-
-version_strategy
-................
-
-**type**: ``string`` **default**: null
-
-The service id of the :doc:`asset version strategy </frontend/custom_version_strategy>`
-applied to the assets.
-
 templating
 ~~~~~~~~~~