Revert of [interpreter] Add string type feedback to add (patchset #3 id:40001 of https://codereview.chromium.org/2392533002/ )

Reason for revert:
Broke the tree again, for no obvious reason :/

Original issue's description:
> [interpreter] Add string type feedback to add
>
> Adds string type feedback to Ignition's AddWithFeedback code stub, for now only
> adding a special case for when both lhs and rhs are strings. This improves
> octane's splay by >100%.
>
> BUG=v8:5400
>
> Committed: https://crrev.com/fb4ae2239d37adaf0321165034050316914de708
> Committed: https://crrev.com/bf1a94f1b269914856a8c8763fd282367f066c67
> Cr-Original-Commit-Position: refs/heads/master@{#39987}
> Cr-Commit-Position: refs/heads/master@{#39996}

TBR=rmcilroy@chromium.org,mythria@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5400

Review-Url: https://codereview.chromium.org/2393193002
Cr-Commit-Position: refs/heads/master@{#40000}