chore: remove custom marshaling of proposal status

[tac0turtle]

Description

Closes: #6787

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Author Checklist

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please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[tac0turtle]

does this need a migration @AmauryM

[codecov]

Codecov Report

Merging #13160 (839dd3a) into main (d47970d) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 839dd3a differs from pull request most recent head 9693bbe. Consider uploading reports for the commit 9693bbe to get more accurate results

@@           Coverage Diff           @@
##             main   #13160   +/-   ##
=======================================
  Coverage   53.72%   53.73%           
=======================================
  Files         645      645           
  Lines       55258    55238   -20     
=======================================
- Hits        29688    29682    -6     
+ Misses      23194    23179   -15     
- Partials     2376     2377    +1     

Impacted Files	Coverage Δ
x/gov/types/v1/proposal.go	17.24% <ø> (+1.36%)	⬆️
x/gov/types/v1/vote.go	28.91% <ø> (+1.64%)	⬆️
x/gov/types/v1beta1/proposal.go	28.36% <ø> (+0.97%)	⬆️
x/gov/types/v1beta1/vote.go	25.97% <ø> (+1.58%)	⬆️
x/staking/simulation/operations.go	74.54% <0.00%> (-1.38%)	⬇️
x/group/keeper/keeper.go	56.25% <0.00%> (-0.40%)	⬇️
crypto/keys/internal/ecdsa/privkey.go	83.01% <0.00%> (+1.88%)	⬆️

[amaury1093]

i don't think we need any migration for this

[amaury1093]

nice!