Fix the MsgModifyNameRequest endpoint to clean up old index entries

[SpicyLemon]

Description

The name module's MsgModifyNameRequest can be used to change the owner of a name. However, the old address -> name index entry isn't being deleted.

This PR:

1. Makes it so that, when a record's address is changing, the old address -> name index entry is deleted.
2. Adds a step to the migration to find and delete any invalid index entries.
3. Fixes the name sims to actually end up doing things.

---

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.
• 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 #1565 (32b6382) into main (4b724a3) will increase coverage by 0.05%.
The diff coverage is 82.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1565      +/-   ##
==========================================
+ Coverage   62.72%   62.78%   +0.05%     
==========================================
  Files         199      199              
  Lines       26122    26188      +66     
==========================================
+ Hits        16386    16443      +57     
- Misses       8636     8642       +6     
- Partials     1100     1103       +3     

Impacted Files	Coverage Δ
x/name/keeper/keeper.go	79.33% <77.27%> (-0.67%)	⬇️
x/name/simulation/operations.go	84.32% <85.71%> (+3.34%)	⬆️
app/upgrades.go	56.64% <100.00%> (+2.56%)	⬆️
x/name/simulation/decoder.go	100.00% <100.00%> (ø)