feature #21889 Deprecate the special SYMFONY__ environment variables (javiereguiluz)

This PR was squashed before being merged into the 3.3-dev branch (closes #21889).

Discussion
----------

Deprecate the special SYMFONY__ environment variables

| Q | A |
| --- | --- |
| Branch? | master |
| Bug fix? | no |
| New feature? | no |
| BC breaks? | no |
| Deprecations? | yes |
| Tests pass? | yes |
| Fixed tickets | #20089 |
| License | MIT |
| Doc PR | - |

Commits
-------

e3362e854c Deprecate the special SYMFONY__ environment variables

Author: fabpot

Tests/Functional/CachePoolsTest.php

@@ -17,16 +17,6 @@
 
 class CachePoolsTest extends WebTestCase
 {
-    protected function setUp()
-    {
-        $_SERVER['SYMFONY__REDIS_HOST'] = getenv('REDIS_HOST');
-    }
-
-    protected function tearDown()
-    {
-        unset($_SERVER['SYMFONY__REDIS_HOST']);
-    }
-
     public function testCachePools()
     {
         $this->doTestCachePools(array(), FilesystemAdapter::class);

Tests/Functional/app/CachePools/redis_config.yml

@@ -1,10 +1,13 @@
 imports:
     - { resource: ../config/default.yml }
 
+parameters:
+    env(REDIS_HOST): 'localhost'
+
 framework:
     cache:
         app: cache.adapter.redis
-        default_redis_provider: "redis://%redis_host%"
+        default_redis_provider: "redis://%env(REDIS_HOST)%"
         pools:
             cache.pool1:
                 public: true

Tests/Functional/app/CachePools/redis_custom_config.yml

@@ -1,12 +1,15 @@
 imports:
     - { resource: ../config/default.yml }
 
+parameters:
+    env(REDIS_HOST): 'localhost'
+
 services:
     cache.test_redis_connection:
         public: false
         class: Redis
         calls:
-            - [connect, ['%redis_host%']]
+            - [connect, ['%env(REDIS_HOST)%']]
 
     cache.app:
         parent: cache.adapter.redis