Refactor IAVL Pruning

[alexanderbez]

Refactor IAVL pruning per the new IAVL API updates, where IAVL handles pruning natively.

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• 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
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[tac0turtle]

should this be documented in the cosmos docs, hub docs or both? I have heard some questions in regard to this. @gamarin2

[fedekunze]

utACK

[AdityaSripal]

ACK 👍

[codecov]

Codecov Report

Merging #5538 into master will decrease coverage by 0.06%.
The diff coverage is 48.27%.

@@            Coverage Diff             @@
##           master    #5538      +/-   ##
==========================================
- Coverage   54.18%   54.12%   -0.07%     
==========================================
  Files         313      313              
  Lines       18963    18949      -14     
==========================================
- Hits        10276    10257      -19     
- Misses       7888     7895       +7     
+ Partials      799      797       -2

Impacted Files	Coverage Δ
client/keys/utils.go	40.35% <ø> (-8.27%)	⬇️
client/context/context.go	2.22% <0%> (-0.02%)	⬇️
x/auth/types/txbuilder.go	23.4% <0%> (ø)	⬆️
client/keys/update.go	73.33% <100%> (ø)	⬆️
client/keys/add.go	42.28% <100%> (ø)	⬆️
client/keys/show.go	83.9% <100%> (ø)	⬆️
client/keys/import.go	68.42% <100%> (ø)	⬆️
client/keys/delete.go	77.27% <100%> (ø)	⬆️
client/keys/list.go	83.33% <100%> (ø)	⬆️
client/keys/export.go	65.21% <100%> (ø)	⬆️
... and 3 more