operations: Fix flakiness due to EOF timeout
In our merge-related tests, we're using testhelper.ReceiveEOFWithTimeout
to wait for the EOF error. If we fail to receive it after more than a
second, then the test fails. It's debatable what the real merit of this
timeout is: the code is not timing sensitive, but we just want to assert
that it does indeed succeed. Furthermore, given our recent shift to use
t.Parallel()
more, we have seen that this timeout may be exceeded on
occasion.
Remove these timeouts and simply assert that we do get an EOF error and drop the now-unused helper function.
Closes #3830 (closed)