Clean up DisablePolicyEthernetRecommendedWorkaround

The experiment has been on by default starting with M121 (CL:5067423)
and enabled server-side starting with M119 (b/271988376).

Remove the experiment.

OBSOLETE_HISTOGRAM[Network.Ethernet.Policy.OncRecommendedFieldsWorkaroundAction]=The corresponding experiment and workaround logic are being removed.

Bug: b:252957425
Change-Id: I3dfe3e8778fdd1fc2611fa20883a6dc7fce9257c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5332814


Reviewed-by: Andreea Costinas <acostinas@google.com>
Reviewed-by: Nikhil Nayunigari <nikhilcn@google.com>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Artyom Chen <artyomchen@google.com>
Reviewed-by: Artem Sumaneev <asumaneev@google.com>
Cr-Commit-Position: refs/heads/main@{#12705916}