Remove prefill estimates scheduler code path

[masih]

Port of the original work done by @udpatil in sei-protocol/sei-cosmos#602

Describe your changes and provide context

Because we established that prefilling estimates doesn't improve performance and have removed it from sei-chain, we can remove the prefillEstimates code path from occ scheduler since its no longer being used.

Testing performed to validate your change

Updated unit tests to remove unnecessary tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.69%. Comparing base (caebdea) to head (3425b1d).
⚠️ Report is 1 commits behind head on main.

❌ Your project status has failed because the head coverage (36.69%) is below the target coverage (60.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2418      +/-   ##
==========================================
+ Coverage   36.66%   36.69%   +0.03%     
==========================================
  Files        1165     1165              
  Lines      104401   104355      -46     
==========================================
+ Hits        38281    38298      +17     
+ Misses      62870    62805      -65     
- Partials     3250     3252       +2     

Files with missing lines	Coverage Δ
sei-cosmos/tasks/scheduler.go	91.32% <ø> (+2.08%)	⬆️
sei-cosmos/x/accesscontrol/keeper/keeper.go	17.94% <ø> (+1.31%)	⬆️

... and 11 files with indirect coverage changes

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