bug #16795 [FrameworkBundle][Validator] Fix apc cache service & config (ogizanagi)

This PR was merged into the 3.0 branch.

Discussion
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[FrameworkBundle][Validator] Fix apc cache service & config

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #16793
| License       | MIT
| Doc PR        | -

_Keep track of https://github.com/symfony/symfony/pull/16794#discussion_r46368928_

_NOTE_: This PR is on standby. If https://github.com/symfony/symfony/pull/16822 is merged, this one might probably be closed, as everything will be done during the merge.

Commits
-------

94a1728 [FrameworkBundle][Validator] Fix apc cache service & config

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php

@@ -454,20 +454,7 @@ class Configuration implements ConfigurationInterface
                     ->info('validation configuration')
                     ->canBeEnabled()
                     ->children()
-                        ->scalarNode('cache')
-                            ->beforeNormalization()
-                                // Can be removed in 3.0, once ApcCache support is dropped
-                                ->ifString()->then(function ($v) {
-                                    if ('apc' === $v) {
-                                        @trigger_error('The ability to pass "apc" as the framework.validation.cache configuration key value is deprecated since version 2.8 and will be removed in 3.0. Use the "validator.mapping.cache.doctrine.apc" service id instead.', E_USER_DEPRECATED);
-
-                                        return 'validator.mapping.cache.apc';
-                                    }
-
-                                    return $v;
-                                })
-                            ->end()
-                        ->end()
+                        ->scalarNode('cache')->end()
                         ->booleanNode('enable_annotations')->defaultFalse()->end()
                         ->arrayNode('static_method')
                             ->defaultValue(array('loadValidatorMetadata'))