increase feemarket's consensus version and add migration handler

[yihuang]

Closes: #1001

Description

Add the migration handler to remove the unused state key.

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #1002 (282ec3d) into main (edf4569) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1002      +/-   ##
==========================================
+ Coverage   59.08%   59.13%   +0.05%     
==========================================
  Files          79       79              
  Lines        6525     6534       +9     
==========================================
+ Hits         3855     3864       +9     
  Misses       2452     2452              
  Partials      218      218              

Impacted Files	Coverage Δ
x/feemarket/keeper/migrations.go	100.00% <100.00%> (ø)

[fedekunze]

LGTM, Can you add tests for the migration?

[yihuang]

LGTM, Can you add tests for the migration?

done, added a unit test.