Positronic brains (and every other mob) using binary chat will no longer send their messages twice.

Fixes: #5444
(cherry picked from commit 75803c5140a6531538bd18c0475a8d580e436e56)
fixes alien castes not understanding each other

only /mob/living/carbon/alien have this var set, so this will not touch anything else.
(cherry picked from commit 5895a098feb003628fd8f6988943bc8775282e82)