remove viper global singleton from x/genutil

[jgimeno]

Description

closes: #XXXX

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• 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
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #6596 into master will decrease coverage by 0.32%.
The diff coverage is 52.20%.

@@            Coverage Diff             @@
##           master    #6596      +/-   ##
==========================================
- Coverage   57.99%   57.66%   -0.33%     
==========================================
  Files         370      493     +123     
  Lines       23551    29621    +6070     
==========================================
+ Hits        13659    17082    +3423     
- Misses       8941    11314    +2373     
- Partials      951     1225     +274     

[alexanderbez]

@jgimeno please rebase this and target against #6599 :)

[alexanderbez]

Looks great @jgimeno! I left a few comments and questions 👍

[alexanderbez]

ACK 🎉

[alexanderbez]

@jgimeno turns out not all viper calls were removed. There is still viper usage in:

• https://github.com/cosmos/cosmos-sdk/blob/master/x/staking/client/cli/tx.go
• https://github.com/cosmos/cosmos-sdk/blob/master/x/staking/client/cli/query.go
• https://github.com/cosmos/cosmos-sdk/blob/master/x/genutil/client/cli/migrate_test.go
• https://github.com/cosmos/cosmos-sdk/blob/master/x/genutil/client/cli/init_test.go