adminSeriesRemove answered the list surface with two h.render calls -- the
row fragment and the out-of-band heading -- and h.render writes a status
line each time, so every removal logged "superfluous
response.WriteHeader call". The heading is an append to a response
already committed, so it now executes straight onto w, the way
writeChromeOOB already does it.
The regression test runs the router under a real server with a captured
ErrorLog: a ResponseRecorder never sees this warning, which is why the
existing removal test did not catch it.
sulthan
c1616b3162