ipv6 mcast: Remove unused macro (MLDV2_QQIC) from mcast.c.

This patch removes  MLDV2_QQIC macro from mcast.c
as it is unused.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>