Respective declarations will explicitly initialise slots
with the hole anyway, so this always was unnecessary.
With varblocks it even became wrong, because block contexts
may now host var bindings, which want undefined.

Fixes the hole leaking when accessing an unitialised,
block-context-allocated var.

R=neis@chromium.org
BUG=571149
LOG=N

Review URL: https://codereview.chromium.org/1584243002

Cr-Commit-Position: refs/heads/master@{#33309}