Remove old GC table name format

[shlomi-noach]

Description

Final step of #14582, removing any and all reference and code support for old GC table name format.

Related Issue(s)

Closes #14582

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

AI Disclosure

[vitess-bot]

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[promptless]

📝 Documentation updates detected!

New suggestion: Update GC table name format documentation for v24

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.78%. Comparing base (1f49de4) to head (dd97341).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #18981   +/-   ##
=======================================
  Coverage   69.77%   69.78%           
=======================================
  Files        1608     1608           
  Lines      214908   214916    +8     
=======================================
+ Hits       149953   149973   +20     
+ Misses      64955    64943   -12     

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