This frees up one bit in FunctionKind, which I plan to make slightly
more syntactic info about functions available in SharedFunctionInfo
(needed for ES2015 Function.name support).

BUG=v8:3956, v8:4760
LOG=n

Review URL: https://codereview.chromium.org/1704223002

Cr-Commit-Position: refs/heads/master@{#34125}