Remove logic for using system libjpeg from libjpeg_turbo gyp file

This is part of simplifying gyp logic for libjpeg. See
http://codereview.chromium.org/10696082.
Review URL: https://chromiumcodereview.appspot.com/10777011

git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/libjpeg_turbo@147428 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
1 file changed