Nullify is already defined in an -inl.h, so there is no need for the
extra functionality (and overhead) of std::function.

Bug: v8:8179
Change-Id: I0b149a962409503a9fde150aa1241de74870533e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1972426Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65494}