node: remove bad fn call and check

These two lines exist because of a screw up on my part while combining
MakeCallback() and MakeDomainCallback().

The reason it never broke core tests is because any paths it would have
broken were rerouted to AsyncWrap::MakeCallback(). The only case that
node::MakeCallback() handles anymore is setImmediate().

Fix: a1da024c "node, async-wrap: remove MakeDomainCallback"
PR-URL: https://github.com/nodejs/io.js/pull/2157


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>