Xml::attr(): remove deprecated code

src/Cms/Helpers.php

@@ -43,13 +43,7 @@ class Helpers
 		// Some of them can be replaced by using `Version` class methods instead
 		// (see method comments). `Content\Translation::contentFile` should be avoided
 		//  entirely and has no recommended replacement.
-		'translation-methods' => true,
-
-		// Passing a single space as value to `Xml::attr()` has been
-		// deprecated. In a future version, passing a single space won't
-		// render an empty value anymore but a single space.
-		// To render an empty value, please pass an empty string.
-		'xml-attr-single-space' => true,
+		'translation-methods' => true
 	];
 
 	/**

src/Toolkit/Xml.php

@@ -97,15 +97,6 @@ public static function attr(
 			return null;
 		}
 
-		// TODO: In 5.0, remove this block to render space as space
-		// @codeCoverageIgnoreStart
-		if ($value === ' ') {
-			Helpers::deprecated('Passing a single space as value to `Xml::attr()` has been deprecated. In a future version, passing a single space won\'t render an empty value anymore but a single space. To render an empty value, please pass an empty string.', 'xml-attr-single-space');
-
-			return $name . '=""';
-		}
-		// @codeCoverageIgnoreEnd
-
 		if ($value === true) {
 			return $name . '="' . $name . '"';
 		}