Remove a nested config reference from the GN build.

Having "config" reference "non_test_config" does nothing. I'm
fixing the warning that will flag this. I checked and a bunch of
targets already add non_test_config, so it isn't obviously
broken otherwise.

TBR=eseidel

Review URL: https://codereview.chromium.org/403653002

git-svn-id: svn://svn.chromium.org/blink/trunk@178459 bbb929c8-8fbe-4397-9dbb-9b2b20218538