- Remove StoreRoot.
- Remove IsObjectJSStringType.
- [ppc, s390] Remove TryInlineTruncateDoubleToI.

R=jarin@chromium.org

Bug: 
Change-Id: I57d739f5b4a8de1d6ffbfb7e85e7d2784bfa4582
Reviewed-on: https://chromium-review.googlesource.com/584828Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46871}