There's no need for them to be in NativeContext.

This CL moves the only remaining Proxy-related SFI.

Bug: v8:10482
Change-Id: I2f5e2d250c30f552787915d306c1be23b9d033bb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2196184Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67766}