chore: simplify and cleanup upgrades.go

[robert-zaremba]

Description

Upgrades.go file got lot of legacy code which is safe to remove. The latest binary can't use it because the existing keepers are not backward compatible. So we are good to remove, and only keep 1-2 examples.

[codecov]

Codecov Report

Merging #2324 (3b7e2fd) into main (7f05ad4) will decrease coverage by 4.77%.
Report is 291 commits behind head on main.
The diff coverage is 66.58%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2324      +/-   ##
==========================================
- Coverage   75.38%   70.62%   -4.77%     
==========================================
  Files         100      170      +70     
  Lines        8025    12872    +4847     
==========================================
+ Hits         6050     9091    +3041     
- Misses       1589     3176    +1587     
- Partials      386      605     +219     

Files	Coverage Δ
ante/ante.go	66.66% <100.00%> (+18.45%)	⬆️
ante/fee.go	80.00% <100.00%> (+1.64%)	⬆️
ante/spam_prevention.go	75.92% <ø> (ø)
app/inflation/inflation.go	100.00% <100.00%> (ø)
app/upgradev3/migrations.go	84.21% <ø> (+5.94%)	⬆️
util/coin/utoken.go	100.00% <100.00%> (ø)
util/ibc/ibc.go	58.82% <ø> (ø)
util/sdkutil/events.go	0.00% <ø> (ø)
util/store/unmarshal.go	42.85% <ø> (ø)
x/incentive/client/tests/suite.go	100.00% <ø> (ø)
... and 40 more

... and 102 files with indirect coverage changes

[gsk967]

LGTM , small suggestion may be we can keep current running upgrade handler