Revert "ES6: Make Map/Set constructors support iterable values"

Reason for revert:
TestSetConstructorIterableValue(WeakSet) fails on x64.debug

TBR=adamk@chromium.org,dslomov@chromium.org
LOG=Y
BUG=

Review URL: https://codereview.chromium.org/461193002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23093 ce2b1a6d-e550-0410-aec6-3dcde31c8c00