DevTools: [Console] do not show separator between command and its result

The patch fixes css to actually avoid showing horizontal delimeter
between user command and its result. This was regressed some time ago.

BUG=416554
R=pfeldman
NOTRY=true

Review URL: https://codereview.chromium.org/591573003

git-svn-id: svn://svn.chromium.org/blink/trunk@182488 bbb929c8-8fbe-4397-9dbb-9b2b20218538