Remove PlatformThread.Mac.*RealtimePeriod histograms

Fixed: 1345366, 1349024
Change-Id: I5d62f90773f0c2f82adb92a4671ce010c576582b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3858112


Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Miriam Zimmerman <mutexlox@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Commit-Queue: Fredrik Hernqvist <fhernqvist@google.com>
Cr-Commit-Position: refs/heads/main@{#1040906}