VectorICs: refactoring to eliminate "for queries only" vector ic mode.

VectorICs: refactoring to eliminate "for queries only" vector ic mode.

Since we need the notion of a dummy vector ic, we can use that to avoid
a special case of the IC constructor. Also, consolidate the two dummy
ICs into one.

BUG=

Review URL: https://codereview.chromium.org/1268783004

Cr-Commit-Position: refs/heads/master@{#29956}