refactor: remove new APIs on x/collection

[0Tech]

Motivation and context

As this module is obsolete, we do not plan to add any more new features.
Security maintenance may continue.

Checklist:

• I followed the contributing guidelines and code of conduct.
• I have added a relevant changelog to CHANGELOG.md
• I have added tests to cover my changes.
• I have updated the documentation accordingly.
• I have updated API documentation client/docs/swagger-ui/swagger.yaml

[codecov]

Codecov Report

Merging #608 (9ca2089) into main (8b9e3e5) will increase coverage by 0.16%.
The diff coverage is 97.31%.

@@            Coverage Diff             @@
##             main     #608      +/-   ##
==========================================
+ Coverage   59.56%   59.72%   +0.16%     
==========================================
  Files         811      811              
  Lines       95263    94747     -516     
==========================================
- Hits        56744    56589     -155     
+ Misses      34974    34674     -300     
+ Partials     3545     3484      -61     

Impacted Files	Coverage Δ
x/collection/codec.go	0.00% <0.00%> (ø)
x/collection/collection.go	80.35% <0.00%> (-1.13%)	⬇️
x/collection/keeper/msg_server.go	74.85% <ø> (+0.92%)	⬆️
x/collection/msgs.go	38.14% <ø> (+6.75%)	⬆️
x/collection/keeper/grpc_query.go	89.58% <80.76%> (-3.13%)	⬇️
x/collection/client/testutil/query.go	100.00% <100.00%> (ø)
x/collection/client/testutil/suite.go	99.60% <100.00%> (+<0.01%)	⬆️
x/collection/client/testutil/tx.go	100.00% <100.00%> (ø)
x/collection/keeper/keys.go	100.00% <100.00%> (ø)
x/collection/keeper/send.go	91.08% <100.00%> (ø)
... and 9 more

[zemyblue]

Please check swagger and statik files.

[0Tech]

Please check swagger and statik files.

It has been applied into #604. This PR must wait for it.