Delete wp_clear_scheduled_hook.php

[IanDelMar]

wp_clear_scheduled_hook.php was added via #127. I missed the fact that the tests are already included in wp_error_parameter.php.

wordpress-stubs/tests/data/wp_error_parameter.php

Lines 102 to 105 in 5e28d4b

	assertType('int<0, max>|false', wp_unschedule_hook('hook'));
	assertType('int<0, max>|false', wp_unschedule_hook('hook', false));
	assertType('int<0, max>|WP_Error', wp_unschedule_hook('hook', true));
	assertType('int<0, max>|WP_Error|false', wp_unschedule_hook('hook', $_GET['wp_error']));