[patch] remove old comment from src/IO/IO.c

[p***@public.gmane.org]

There is an outdated comment in src/IO/IO.c. hg blame src/IO/IO.c also
shows that it is older than the code.

This patch removes comment.

#defines are similar to SHUT_RD, SHUT_WR and SHUT_RDWR, but shutdown
is not used: code just dCloses descriptor when both sides are asked to
be closed.