net/http/httptest: delete TestIssue7264

net/http/httptest: delete TestIssue7264

Now it's failing on Windows:

panic: httptest: failed to listen on a port: listen tcp 127.0.0.1:0:
listen: An operation on a socket could not be performed because the
system lacked sufficient buffer space or because a queue was full.

Since we can't seem to understand what the test is trying to test,
and because it is causing problems on multiple systems,
delete it.

Fixes #7264.

TBR=bradfitz
CC=brainman, golang-codereviews
https://golang.org/cl/141210043