refactor: cleanup simapp

[julienrbrt]

Description

As simapp must not be imported and helpers have been extracted to testutil/sims`
Removes unnecessary helpers from SimApp.

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Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
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]

This not used anymore?

[julienrbrt]

This not used anymore?

A few isn't. They can be replaced with helpers from using keepers directly.

[codecov]

Codecov Report

Merging #13757 (ad8db04) into main (08be7ee) will decrease coverage by 0.21%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13757      +/-   ##
==========================================
- Coverage   56.15%   55.93%   -0.22%     
==========================================
  Files         655      656       +1     
  Lines       56195    57141     +946     
==========================================
+ Hits        31555    31961     +406     
- Misses      22064    22598     +534     
- Partials     2576     2582       +6     

Impacted Files	Coverage Δ
simapp/test_helpers.go	34.30% <ø> (ø)
testutil/sims/app_helpers.go	0.00% <ø> (ø)
tx/textual/valuerenderer/duration.go
tx/textual/valuerenderer/coins.go
tx/textual/valuerenderer/string.go
tx/textual/valuerenderer/valuerenderer.go
tx/textual/valuerenderer/dec.go
tx/textual/valuerenderer/int.go
tx/textual/valuerenderer/bytes.go
tx/textual/valuerenderer/timestamp.go
... and 12 more