src: remove old code

The Socket writable only change was added and implemented in the
constructor around 5885f464, but this was never removed.

The libev counter issue is no longer prudent; the test remains in
test/sequential/test-regress-GH-1726.

PR-URL: https://github.com/nodejs/io.js/pull/1819


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>