Use newInstanceWithoutConstructor when available.

Changed ClassMetadataInfo::newInstance to always use ReflectionClass::newInstanceWithoutConstructor when available, not just for specific versions. 

As discussed here: https://github.com/doctrine/doctrine2/commit/530c01b5e3ed7345cde564bd511794ac72f49b65#commitcomment-6635975
I believe it is better because versions change, it is easy to forget a corner case (ex: 5.5.13, 5.4.29, etc.), support may be added in earlier branches and it obscures the fact that what you want is the support for a specific method. If that's what you want, test for it. [Modernizr](http://modernizr.com/) has been advocating this for ages. The Zend implementation is not the only one, there is for example HHVM.

Using versions is faster and may be preferable in some cases, but this is not a performance critical path as the prototype is cached.

If you really need to add a version check, there should be a comment saying why. Is the serialization support that changed or the ReflectionClass that changed? Using feature testing, it is clear that you would prefer to use the feature, but you have a fallback if it is not available.