Cleanup [SetWrapperReferenceFromReference] cruft
Cleanup [SetWrapperReferenceFromReference] cruft

Followup to:
Kill [SetWrapperReferenceFromReference] IDL extended attribute
https://codereview.chromium.org/181513002/

TBR=haraken
BUG=345503

Review URL: https://codereview.chromium.org/176993007

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@168259 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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