Do not poison %FunctionPrototype%'s restricted properties

In ES6, these properties of the intrinsic %FunctionPrototype% are poisoned during
CreateIntrinsics() / AddRestrictedFunctionProperties(). It's unnecessary to poison them
again, and testing whether they are a function or not causes tests to fail.

BUG=v8:3982
R=arv@chromium.org

Review URL: https://codereview.chromium.org/1067223002

Cr-Commit-Position: refs/heads/master@{#324265}
1 file changed