minor symfony#59395 Remove comment about AppVeyor in phpunit (alexandre-daubois)

This PR was merged into the 6.4 branch.

Discussion
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Remove comment about AppVeyor in `phpunit`

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Follow-up for symfony#59394. Removes a now-necessary comment. It is the last occurrence of AppVeyor in the codebase.

Commits
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fb56611 Remove comment about AppVeyor in `phpunit`

Author: nicolas-grekas

phpunit

@@ -1,10 +1,6 @@
 #!/usr/bin/env php
 <?php
 
-// Cache-Id: 2021-05-27 20:30 UTC
-// For caching to work properly on appveyor, this file
-// must be exactly the same in all maintained branches
-
 if (!file_exists(__DIR__.'/vendor/symfony/phpunit-bridge/bin/simple-phpunit')) {
     echo "Unable to find the `simple-phpunit` script in `vendor/symfony/phpunit-bridge/bin/`.\nPlease run `composer update` before running this command.\n";
     exit(1);