refactor(`app`): remove deprecated rest imports

[aljo242]

What does this PR does?

Removes deprecated rest associated imports in app.go. This is to prepare for their being removed in Cosmos SDK v0.46.x.

Part of #909

Checklist

These are the criteria that every PR should meet, please check them off as you review them:

• [ ] Include tests
• [ ] Respect code style and lint
• [ ] Update documentation (*.md) (if needed)

[codecov[bot]]

Codecov Report

Merging #908 (129df05) into develop (d55fd30) will increase coverage by 0.00%. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #908   +/-   ##
========================================
  Coverage    10.56%   10.57%           
========================================
  Files          327      327           
  Lines        75110    75110           
========================================
+ Hits          7939     7941    +2     
+ Misses       66982    66981    -1     
+ Partials       189      188    -1     

Impacted Files	Coverage Δ
x/campaign/simulation/store.go	84.45% <0.00%> (+1.35%)	:arrow_up: