Revert "Add a RELEASE_ASSERT to guard against duplicates in DOMWrapperMap"

This reverts r153736, as there still seem to be enough world leaks in
the wild for the release assert to be the top crasher.

TBR=abarth
BUG=260011

Review URL: https://codereview.chromium.org/19258002

git-svn-id: svn://svn.chromium.org/blink/trunk@154239 bbb929c8-8fbe-4397-9dbb-9b2b20218538