Revert of [stubs] Port SubStringStub to TurboFan (patchset #8 id:140001 of https://codereview.chromium.org/2355793003/ )

Reason for revert:
Speculative revert because of stability problems

Original issue's description:
> [stubs] Port SubStringStub to TurboFan
>
> This ports the platform-specific SubStringStub to TurboFan.
>
> It also contains a minor bug-fix for the case when the requested substring
> length equals the subject string length, but the start index is not equal to 0.
> The old stub implementation returned the subject string, while the new
> implementation calls into runtime, which finally results in a thrown exception.
>
> BUG=v8:5415
>
> Committed: https://crrev.com/49be31921536716706a6790fbbf9c346b975af16
> Cr-Commit-Position: refs/heads/master@{#39653}

TBR=ishell@chromium.org,bmeurer@chromium.org,jgruber@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=v8:5415, chromium:649967
NOPRESUBMIT=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2365413002
Cr-Commit-Position: refs/heads/master@{#39737}