Do not append webkit/tools/layout_tests to path.

We are removing webkit/ layer, so we don't need to point to this path
anymore. Also the test expectations files were moved to content/test/
directory already.

BUG=338338
TEST=None
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/581013002

git-svn-id: svn://svn.chromium.org/blink/trunk@182294 bbb929c8-8fbe-4397-9dbb-9b2b20218538