scripts: remove unused --feeder-url from take_nodes_out_of_observer_mode

[ShahakShama]

The fetched block number was only used as a soft filter on the post-restart
logs URL. Drop the flag and the related dead plumbing, and refresh the script
title/help text to describe what the script actually does.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

[reviewable-StarkWare]

This change is 

[ShahakShama]

• scripts: remove unused --feeder-url from take_nodes_out_of_observer_mode #14008 👈 (View in Graphite)
• main

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PR Summary

Low Risk
Low risk refactor of an operational script: it only changes CLI arguments and the log-explorer query filter, without altering the actual config update/restart behavior.

Overview
Updates scripts/prod/take_nodes_out_of_observer_mode.py to remove the --feeder-url flag and all block-number fetching/printing, since it was only used to soft-filter the post-restart logs link.

The script now generates a logs-explorer URL based solely on the DECISION_REACHED proposer match, and refreshes the CLI description/usage examples to reflect taking nodes out of observer mode via --validator-id-start-from + restart.

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[matanl-starkware]

@matanl-starkware reviewed 1 file and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on ShahakShama).