Remove x/mock

[alexanderbez]

Description

Remove x/mock in favor of SimApp. Each module should also be careful to have its unit tests be contained under the package {module}_test to avoid import cycles and dependency hell.

Note, there still exist modules where the keeper (integration/unit) tests still create ad-hoc applications. These need to be refactored in order to:

1. Have package renamed (to {module}_test)
2. Use simapp

ref: #4875

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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 #5642 into master will not change coverage.
The diff coverage is 14.28%.

@@           Coverage Diff           @@
##           master    #5642   +/-   ##
=======================================
  Coverage   40.49%   40.49%           
=======================================
  Files         323      323           
  Lines       27134    27134           
=======================================
  Hits        10987    10987           
  Misses      15085    15085           
  Partials     1062     1062

Impacted Files	Coverage Δ
x/auth/client/query.go	0% <0%> (ø)	⬆️
x/gov/client/utils/query.go	24.36% <20%> (ø)	⬆️