The old code was using VariableMode, but that signal is both
over-pessimistic (some CONST and LET variables need no hole-initialization)
and inconsistent with other uses of the InitializationFlag enum (such
as %LoadLookupSlot).

This changes no observable behavior, but removes unnecessary hole
initialization and hole checks in a few places, including
block-scoped function declarations, super property lookups,
and new.target.

R=bmeurer@chromium.org, neis@chromium.org

Review-Url: https://codereview.chromium.org/2201193004
Cr-Commit-Position: refs/heads/master@{#38395}