Revert "[iOS][macOS] Prevent histogram files from getting backed up"

This reverts commit e77f168f5c1cf62a32943cc6fc9d0b9ae682b310.

Reason for revert: This caused a 1.4s startup time regression on
macOS. We need to find a better point in time to schedule this
work, or send it to a background thread. But since a fix needs to
be merged to Beta, the best fix is to revert.



Original change's description:
> [iOS][macOS] Prevent histogram files from getting backed up
>
> The histogram "spare" file is several megabtyes in size, and isn't
> useful to back up and restore, since it only exists to save time
> on the next startup. Similarly, the file used to store metrics
> isn't useful to backup either, since the metrics it contains will,
> in most cases, already have been uploaded before the backup is ever
> restored.
>
> This is particularly significant in the case where backups are saved in
> the cloud (e.g., iCloud backup on iOS), since large files use up
> bandwidth and cloud storage.
>
> This CL prevents backing up these histogram files on Apple platforms,
> where we have APIs to decide which files get backed up.
>
> Bug: 1265580
> Change-Id: Icbe83926962e0ea9b30e04fd930530f915105013
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3321246
> Reviewed-by: Brian White <bcwhite@chromium.org>
> Commit-Queue: Ali Juma <ajuma@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#950098}

Bug: 1265580, 1299907
Change-Id: I3e266d58d70a132c751beae6812b0f77335cf1dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3482098
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Ali Juma <ajuma@chromium.org>
Cr-Commit-Position: refs/heads/main@{#974176}