Do not suggest all_webkit to users.

all_webkit will be removed soon from Chromium and is just an alias to
blink_tests.

This was discussed in this thread:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/s3VeTNMy85M/Fjj76zoN3LkJ

And renamed here:
https://codereview.chromium.org/59233012

BUG=None
TEST=None
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/191973002

git-svn-id: svn://svn.chromium.org/blink/trunk@168789 bbb929c8-8fbe-4397-9dbb-9b2b20218538