DevTools: remove leftover test expectation forgotten after test removal

Remove css-setStyleText-expected.txt. The corresponding testcase was
removed in r166503

BUG=
TBR=pfeldman

Review URL: https://codereview.chromium.org/155513009

git-svn-id: svn://svn.chromium.org/blink/trunk@166633 bbb929c8-8fbe-4397-9dbb-9b2b20218538