net: remove noisy test for issue 3590

The test for issue 3590 causes an error to be printed to stderr when run (although the error is obscured during go test std). This is confusing for people who get breakage in the net package as the error is harmless and most likely unrelated to their build breakage.

Given the way the test works, by reaching into the guts of the netFD, I can't see a way to silence the error without adding a bunch of code to support the test, therefore I am suggesting the test be removed before Go 1.1 ships.

R=alex.brainman, mikioh.mikioh, rsc
CC=golang-dev
https://codereview.appspot.com/7307110