Kill [SetWrapperReferenceFromReference] IDL extended attribute

Kill [SetWrapperReferenceFromReference] IDL extended attribute to reduce the
complexity of our IDL and of our bindings generators. We now use only
[SetWrapperReferenceFrom] IDL extended attribute and the generated bindings
code will accept that the implementation returns either a reference or a
pointer (by constructing using WTF::getPtr()).

R=haraken, adamk

Review URL: https://codereview.chromium.org/181513002

git-svn-id: svn://svn.chromium.org/blink/trunk@168048 bbb929c8-8fbe-4397-9dbb-9b2b20218538