validator: Remove --dev-halt-at-slot argument

[steviez]

Summary of Changes

This was a debug flag to stop the validator midway through startup; it has no value now so remove the underlying logic and mark the flag as deprecated

The flag was added prior to 8b2327e (2019); I didn't care to go digging further but I think its time has come

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.6%. Comparing base (0d5dfb0) to head (9d3bb5f).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9220   +/-   ##
=======================================
  Coverage    82.6%    82.6%           
=======================================
  Files         890      890           
  Lines      320910   320889   -21     
=======================================
- Hits       265294   265291    -3     
+ Misses      55616    55598   -18     

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• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[t-nelson]

can you split deprecation and removal so we can bp the deprecation and let the removal ride 4.0

[steviez]

can you split deprecation and removal so we can bp the deprecation and let the removal ride 4.0

Wasn't planning on BP'ing but if you're on board then let's do it - #9232 is the PR that is suitable for BP. Will rebase this one on top of master once it lands. Will request review from ya on that one once CI completes

[t-nelson]

well if you want to remove on a major, it needs deprecated before the previous minor hits mb

[steviez]

well if you want to remove on a major, it needs deprecated before the previous minor hits mb

Fair enough - I figured this was functionally dead so ripped it + left the flag to avoid someone erroring out. Probably a bit too aggressive and better to do The-Right-Thing™️ instead. PR has been rebased on tip + updated, we should seemingly land the BP before this one

[steviez]

Extra force push was for a CI failure that I was pretty confident was unrelated to my change (gossip); green CI now so I think we're good

[steviez]

we should seemingly land the BP before this one

#9244 merged so this is done

[t-nelson]

ah sry missed the rebase here