Remove dead code written for PHP 5.2
diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 04445f5..25dc0d4 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -1216,18 +1216,7 @@
 			$str = 'ipv6.host'.substr($str, strlen($matches[1]) + 2);
 		}
 
-		$str = 'http://'.$str;
-
-		// There's a bug affecting PHP 5.2.13, 5.3.2 that considers the
-		// underscore to be a valid hostname character instead of a dash.
-		// Reference: https://bugs.php.net/bug.php?id=51192
-		if (version_compare(PHP_VERSION, '5.2.13', '==') OR version_compare(PHP_VERSION, '5.3.2', '=='))
-		{
-			sscanf($str, 'http://%[^/]', $host);
-			$str = substr_replace($str, strtr($host, array('_' => '-', '-' => '_')), 7, strlen($host));
-		}
-
-		return (filter_var($str, FILTER_VALIDATE_URL) !== FALSE);
+		return (filter_var('http://'.$str, FILTER_VALIDATE_URL) !== FALSE);
 	}
 
 	// --------------------------------------------------------------------