test: remove unused simapp tests

[colin-axner]

Description

Removes all _test.go files in simapp directory as these are currently untested. These files were initially copied from the SDK, but have not been added to our testing workflow and do not add any additional code coverage that the SDK doesn't have. They have been removed to ease maintenance burden

closes: #4167

Commit Message / Changelog Entry

type: commit message

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• 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 and Go style guide.
• Wrote unit and integration tests.
• Updated relevant documentation (docs/) or specification (x/<module>/spec/).
• Added relevant godoc comments.
• Provide a commit message to be used for the changelog entry in the PR description for review.
• Re-reviewed Files changed in the Github PR explorer.
• Review Codecov Report in the comment section below once CI passes.

[damiannolan]

gladly

[crodriguezvega]

🧼