test: remove two obsolete pummel tests

Remove two tests that assume creating big buffers fails.  The size limit
is twice as big on 64 bits architectures now and is going to be removed
completely in the not too distant future.

PR-URL: https://github.com/nodejs/io.js/pull/2022


Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>