PHP 8.2: fix dynamic property

Looks like the `Parser::$stringDateTimes` property was removed in commit 7895e56, which was part of the `0.2.0` release, so setting this non-declared property from the tests has no function.

Removing the property setting fixes the PHP 8.2 "Creation of dynamic property Mf2\Parser::$stringDateTimes is deprecated" deprecation notices.

Author: jrfnl

tests/Mf2/CombinedMicroformatsTest.php

@@ -66,7 +66,6 @@ public function testHEventLocationHCard() {
 }';
 
 		$parser = new Parser($input, '', true);
-		$parser->stringDateTimes = true;
 		$output = $parser->parse();
 
 		$this->assertJsonStringEqualsJsonString(json_encode($output), $expected);
@@ -96,7 +95,6 @@ public function testHCardOrgPOrg() {
 }';
 
 		$parser = new Parser($input, '', true);
-		$parser->stringDateTimes = true;
 		$output = $parser->parse();
 
 		$this->assertJsonStringEqualsJsonString(json_encode($output), $expected);
@@ -135,7 +133,6 @@ public function testHCardOrgHCard() {
 }';
 
 		$parser = new Parser($input, '', true);
-		$parser->stringDateTimes = true;
 		$output = $parser->parse();
 
 		$this->assertJsonStringEqualsJsonString(json_encode($output), $expected);