src: remove unnecessary template parameter

The template class information is received via the type of the first
argument. So there is no need to use Wrap<T>(handle).

PR-URL: https://github.com/joyent/node/pull/8110


Signed-off-by: Trevor Norris <trev.norris@gmail.com>
Reviewed-by: Fedor Indutny <fedor@indutny.com>
Reviewed-by: Alexis Campailla <alexis@janeasystems.com>
Reviewed-by: Julien Gilli <julien.gilli@joyent.com>