This is a reland of 048a3a3e

Original change's description:
> [Intl] Cleans up intl-relative-time-format flag
> 
> Cleans up always=true intl-relative-time-format flag
> It shipped in m71 in Dec 2018.
> 
> Bug: v8:8704
> Change-Id: I52d86aea9aedf201a216a1df0773a486fbee37b9
> Reviewed-on: https://chromium-review.googlesource.com/c/1417299
> Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> Commit-Queue: Frank Tang <ftang@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#58904}

Bug: v8:8704
Change-Id: I0b3c58b89a81200e9ac8303494317d21d8936319
Reviewed-on: https://chromium-review.googlesource.com/c/1420360Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59475}