Previously, both type feedback vector and the shared function info
of a function points to the matching type feedback metadata. This
makes finding the shared function info of a type feedback vector
difficult.

Instead, we now point the type feeback vector to the shared function
info, and find the metadata through the shared function info.

Also remove the obsolete empty type feedback vector.

R=hpayer@chromium.org, mvstanton@chromium.org
BUG=v8:5808

Review-Url: https://codereview.chromium.org/2672363002
Cr-Commit-Position: refs/heads/master@{#43026}