minor symfony#51044 [Form] Fix form events phpdocs (HeahDude)

This PR was merged into the 5.4 branch.

Discussion
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[Form] Fix form events phpdocs

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | ~
| License       | MIT
| Doc PR        | ~

Sibling of symfony/symfony-docs#18587.

Commits
-------

2032b5b [Form] Fix form events phpdocs

Author: nicolas-grekas

src/Symfony/Component/Form/Event/PostSetDataEvent.php

@@ -16,7 +16,8 @@
 /**
  * This event is dispatched at the end of the Form::setData() method.
  *
- * This event is mostly here for reading data after having pre-populated the form.
+ * It can be used to modify a form depending on the populated data (adding or
+ * removing fields dynamically).
  */
 final class PostSetDataEvent extends FormEvent
 {

src/Symfony/Component/Form/Event/PreSetDataEvent.php

@@ -16,9 +16,7 @@
 /**
  * This event is dispatched at the beginning of the Form::setData() method.
  *
- * It can be used to:
- *  - Modify the data given during pre-population;
- *  - Modify a form depending on the pre-populated data (adding or removing fields dynamically).
+ * It can be used to modify the data given during pre-population.
  */
 final class PreSetDataEvent extends FormEvent
 {