Store maps on the CheckMaps operator instead of burning inputs for
the individual maps. Use the same data structure (the ZoneHandleSet)
in the LoadElimination to track multiple maps per object.

BUG=v8:5267
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2431563002
Cr-Commit-Position: refs/heads/master@{#42010}