[x/gamm][Refactor] Follow-on cleanup to Gamm Refactor

[ValarDragon]

Followup cleanup from the gamm refactor, now deleting unused code, and shuffling around where structs are defined, and if functions are publicly exposed. This PR has no logic updates, it just moves definitions around.

It should be reviewable commit by commit.

• deletes math.go and math_test.go. math_test's intended logic should imo be re-written from scratch for balancer types, it did not really seem like it had a useful form to me.
• delete the legacy pool interface
• Move event creation to types/events.go
• Move poolasset.pb.go to pool-models/balancer
• Move balancer weight validation constants & function

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

[codecov-commenter]

Codecov Report

Merging #1129 (e4bc4ed) into main (f1389ee) will increase coverage by 0.28%.
The diff coverage is 39.68%.

@@            Coverage Diff             @@
##             main    #1129      +/-   ##
==========================================
+ Coverage   19.90%   20.19%   +0.28%     
==========================================
  Files         200      199       -1     
  Lines       25498    25062     -436     
==========================================
- Hits         5076     5061      -15     
+ Misses      19515    19074     -441     
- Partials      907      927      +20     

Impacted Files	Coverage Δ
osmomath/math.go	64.44% <0.00%> (-1.47%)	⬇️
x/gamm/client/cli/query.go	42.26% <ø> (+3.71%)	⬆️
x/gamm/keeper/grpc_query.go	39.58% <ø> (+0.80%)	⬆️
x/gamm/keeper/invariants.go	0.00% <0.00%> (ø)
x/gamm/keeper/keeper.go	60.86% <ø> (-20.39%)	⬇️
x/gamm/keeper/pool.go	68.00% <ø> (ø)
x/gamm/pool-models/balancer/marshal.go	78.57% <ø> (ø)
x/gamm/pool-models/balancer/tx.pb.go	0.77% <0.00%> (ø)
x/gamm/types/events.go	0.00% <0.00%> (ø)
x/gamm/types/pool.go	0.00% <ø> (ø)
... and 14 more

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[alexanderbez]

Don't have much context here, but it seems like we just moved things around for clarity and better architecture, so LGTM 👍

[ValarDragon]

Thanks for pushing for more docs, added some for everything you pointed out!

[alexanderbez]