refactor: Use mocks for x/feegrant testing

[facundomedica]

Description

Ref: #12398

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• confirmed the correct type prefix in the PR title
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[tac0turtle]

lgtm, do we need to revert simulation changes

[codecov]

Codecov Report

Merging #12472 (f1b2405) into main (401d17b) will decrease coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main   #12472      +/-   ##
==========================================
- Coverage   65.29%   65.21%   -0.08%     
==========================================
  Files         694      694              
  Lines       71851    71850       -1     
==========================================
- Hits        46917    46859      -58     
- Misses      22295    22355      +60     
+ Partials     2639     2636       -3     

Impacted Files	Coverage Δ
x/feegrant/keeper/keeper.go	79.14% <ø> (-1.79%)	⬇️
x/feegrant/keeper/migrations.go	0.00% <0.00%> (-50.00%)	⬇️
x/feegrant/module/module.go	13.48% <0.00%> (-31.47%)	⬇️
x/feegrant/genesis.go	0.00% <0.00%> (-16.67%)	⬇️
x/distribution/simulation/operations.go	80.85% <0.00%> (-9.58%)	⬇️
crypto/keys/internal/ecdsa/privkey.go	81.13% <0.00%> (-1.89%)	⬇️

[facundomedica]

lgtm, do we need to revert simulation changes

No, those changes are ok. I removed some dependencies and stopped using the staking keeper which was there for no good reason