[FedCM] Clean up the FedCmCooldownOnIgnore Finch experiment code

The experiment is terminated so this patch cleans up the logic from the
code base. In particular, it uses git revert on the following 3 CLs:
  1. crrev.com/c/6297528
  2. crrev.com/c/6299895
  3. crrev.com/c/6344733

Bug: 398888508
Change-Id: I69099e6c345f7583299f6682ab522430f01e8344
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6851470
Reviewed-by: Nicolás Peña <npm@chromium.org>
Reviewed-by: Ravjit Uppal <ravjit@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1502716}