[CLEANUP] Remove impossible conditional

The parameter `$parserState` is specified to be a `ParserState`, so it can
never be a string.

Author: JakeQZ

config/phpstan-baseline.neon

@@ -1,11 +1,5 @@
 parameters:
 	ignoreErrors:
-		-
-			message: '#^Call to function is_string\(\) with Sabberworm\\CSS\\Parsing\\ParserState will always evaluate to false\.$#'
-			identifier: function.impossibleType
-			count: 1
-			path: ../src/CSSList/CSSList.php
-
 		-
 			message: '#^Loose comparison via "\=\=" is not allowed\.$#'
 			identifier: equal.notAllowed

src/CSSList/CSSList.php

@@ -64,9 +64,6 @@ public function __construct(?int $lineNumber = null)
     public static function parseList(ParserState $parserState, CSSList $list): void
     {
         $isRoot = $list instanceof Document;
-        if (\is_string($parserState)) {
-            $parserState = new ParserState($parserState, Settings::create());
-        }
         $usesLenientParsing = $parserState->getSettings()->usesLenientParsing();
         $comments = [];
         while (!$parserState->isEnd()) {