timers: don't close interval timers when unrefd

This change fixes a regression introduced by commit
0d051238be2e07e671d7d9f4f444e0cc1efadf1b, which contained a typo that
would cause every unrefd interval to fire only once.

Fixes #8900.

Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-by: Trevor Norris <trev.norris@gmail.com>
src: re-add 1024-bit SSL certs removed by f9456a2

this fixes a problem where connecting to AWS services
would report an untrusted cert error.

Fixes: https://github.com/joyent/node/issues/8894
PR-URL: https://github.com/joyent/node/pull/8904
Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>
Reviewed-By: Julien Gilli <julien.gilli@joyent.com>