Since enabling destructuring already implies enabling default parameters,
there's not a good way to separate these two. Luckily, they're both
feature-complete (save for destructuring assignment).

This causes us to pass an additional 24 test262 tests.

BUG=v8:811, v8:2160
LOG=y

Review URL: https://codereview.chromium.org/1407393009

Cr-Commit-Position: refs/heads/master@{#31844}