Remove socket.h include from debug.h

Looks like there is no Socket usage in debug.h, so we don't need to
include it there.

TEST=in static build, ninja -C out/Debug/ d8
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/120933003

Patch from Thiago Farina <tfarina@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18459 ce2b1a6d-e550-0410-aec6-3dcde31c8c00