Add $ before url_prefix_len to make it a variable. (#3668)

* Add $ before url_prefix_len to make it a variable.

* Remove unnecessary string length check

* Remove useless $type_url_len

php/src/Google/Protobuf/Any.php

@@ -207,16 +207,14 @@ class Any extends \Google\Protobuf\Internal\Message
     public function unpack()
     {
         // Get fully qualifed name from type url.
-        $type_url_len = strlen($this->type_url);
         $url_prifix_len = strlen(Any::TYPE_URL_PREFIX);
-        if ($type_url_len < url_prifix_len ||
-            substr($this->type_url, 0, $url_prifix_len) !=
+        if (substr($this->type_url, 0, $url_prifix_len) !=
                 Any::TYPE_URL_PREFIX) {
             throw new \Exception(
                 "Type url needs to be type.googleapis.com/fully-qulified");
         }
         $fully_qualifed_name =
-            substr($this->type_url, $url_prifix_len, $type_url_len);
+            substr($this->type_url, $url_prifix_len);
 
         // Create message according to fully qualified name.
         $pool = DescriptorPool::getGeneratedPool();