VectorICs: megamorphic keyed loads in crankshaft don't need a vector.

This needs "Pass load ic state through the Oracle"
(https://codereview.chromium.org/1083933002/) to land first.

BUG=
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/1083083002

Cr-Commit-Position: refs/heads/master@{#27827}