[MEDIUM] remove unused references to {CL|SV}_STSHUT*

[MEDIUM] remove unused references to {CL|SV}_STSHUT*

All references to CL_STSHUT* and SV_STSHUT* were removed where
possible. Some of them could not be removed because they are
still in use by the unix sockets.

A bug remains at this stage. Injecting with a very short timeout
sometimes leads to a client in close state and a server in data
state with all buffer flags indicating a shutdown but the server
fd still enable, thus causing a busy loop.