bug #32868 [PhpUnitBridge] Allow symfony/phpunit-bridge > 4.2 to be i…

…nstalled with phpunit 4.8 (jderusse)

This PR was merged into the 3.4 branch.

Discussion
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[PhpUnitBridge] Allow symfony/phpunit-bridge > 4.2 to be installed with phpunit 4.8

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | NA
| License       | MIT
| Doc PR        | NA

phpunit/phpunit 4.8 defined the composer.json config.platform to php 5.3 which is not compatible with symfony/phpunit-bridge > 4.2

This PR removes the config from composer.json

Commits
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a0f68aa Fix symfony/phpunit-bridge not up to date in phpunit 4.8 test suite

src/Symfony/Bridge/PhpUnit/bin/simple-phpunit

@@ -83,6 +83,8 @@ if (!file_exists("$PHPUNIT_DIR/phpunit-$PHPUNIT_VERSION/phpunit") || md5_file(__
     if (5.1 <= $PHPUNIT_VERSION && $PHPUNIT_VERSION < 5.4) {
         passthru("$COMPOSER require --no-update phpunit/phpunit-mock-objects \"~3.1.0\"");
     }
+
+    passthru("$COMPOSER config --unset platform");
     if (file_exists($path = $root.'/vendor/symfony/phpunit-bridge')) {
         passthru("$COMPOSER require --no-update symfony/phpunit-bridge \"*@dev\"");
         passthru("$COMPOSER config repositories.phpunit-bridge path ".escapeshellarg(str_replace('/', DIRECTORY_SEPARATOR, $path)));