Revert "gyp: use all processors instead of hard-coded 8."

This reverts commit 56a70c5641bbb01683dfeb7aa8a65800a00fb936.

The change made bug 112 trigger on a trybot since we used
fewer processes, making bug 112 easier to trigger. The
value of this patch is not big enough to fuss around.

BUG=
R=torne@chromium.org

Review URL: https://codereview.chromium.org/265003004

git-svn-id: http://gyp.googlecode.com/svn/trunk@1911 78cadc50-ecff-11dd-a971-7dbc132099af