chore: remove unused local variables (backport #22340)

[mergify]

Description

Closes: #XXXX

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Summary by CodeRabbit

• New Features

  • Enhanced error logging for key-value store iterator closure.
  • Improved test coverage for cache and mempool functionalities, including new test cases for transaction ordering and cache behavior.

• Bug Fixes

  • Streamlined logic for handling delegations in the staking keeper.

• Tests

  • Added multiple new test functions for CacheKVStore and priority nonce mempool.
  • Improved validation logic and concurrency tests for transaction handling.

• Documentation

  • Updated comments and documentation for clarity in test cases and methods.

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This is an automatic backport of pull request #22340 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 1515856 has failed:

On branch mergify/bp/release/v0.52.x/pr-22340
Your branch is up to date with 'origin/release/v0.52.x'.

You are currently cherry-picking commit 151585656.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .golangci.yml
	modified:   simapp/export.go
	modified:   types/mempool/priority_nonce_test.go
	modified:   x/staking/keeper/query_utils.go

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   store/cachekv/store_test.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally