Revert "net: Avoid tickDepth warnings on small writes"

This commit breaks simple/test-stream2-stderr-sync.  Need to figure out
a better way, or just accept that `(function W(){stream.write(b,W)})()`
is going to be noisy.  People should really be using the `'drain'` event
for this use-case anyway.

This reverts commit 02f7d1bf.