MINOR: sink: Remove useless test on SE_FL_SHR/SHW flags

MINOR: sink: Remove useless test on SE_FL_SHR/SHW flags

Re-apply dcd917d972 ("MINOR: applet: Remove uselelss test on SE_FL_SHR/SHW
flags") for sink_forward_oc_io_handler() function as it was probably
overlooked given that sink_forward_oc_io_handler() and
sink_forward_io_handler() follow the same logic.

(cherry picked from commit f2848e6146faa0794a9878610602d03608af07df)
[ada: required to fix applet not destroyed upon server disconnect,
 see GH #3153, the test turned out to be mandatory, not useless]
Signed-off-by: Aurelien DARRAGON <adarragon@haproxy.com>