I recently modified tabwriter to reduce the number of defers due to
flush calls. However, I forgot to notice that the new function
flushNoDefers can no longer return an error, due to the lack of the
defer.
In crypto/tls, hashForServerKeyExchange never returned a non-nil error,
so simplify the code.
Finally, in go/types and net we can find a few trivially unused
parameters, so remove them.