As noticed by jkummerow@ there's probably not really a point in
keeping two separate runtime functions that perform the same
operation, but one has a different fast-path (which is not
available to the other). So %KeyedGetProperty is now effectively
%GetProperty and used consistently as fallback from both the ICs
as well as other callers like the GetProperty builtin.

Bug: v8:8015
Change-Id: Ib46b13da739229e2eb820ecf87923ac99c6971d3
Reviewed-on: https://chromium-review.googlesource.com/1199105
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55547}