Revert "fixed makeDisposition"

This reverts commit e7cba0bd3a3c9b3d891741da116953aa5a36cc22.
Changed instances of \DateTimeZone::UTC to 'UTC' as the constant is not valid a produces this error when DateTimeZone is instantiated: DateTimeZone::__construct() [<a href='datetimezone.--construct'>datetimezone.--construct</a>]: Unknown or bad timezone (1024)

backport ffdc5af68075b9e2911f7f19b23faa0558637c12

Conflicts:
	src/Symfony/Component/Form/Extension/Core/ChoiceList/MonthChoiceList.php
	tests/Symfony/Tests/Component/Form/Extension/Core/ChoiceList/MonthChoiceListTest.php