chore: clean up code for legacy frontend

[xxchan]

What's changed and what's your intention?

as title

Checklist

• [ ] I have written necessary docs and comments
• [ ] I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #3181 (c9b01f8) into main (b7537bb) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main    #3181   +/-   ##
=======================================
  Coverage   73.59%   73.59%           
=======================================
  Files         744      744           
  Lines      102029   102025    -4     
=======================================
- Hits        75091    75089    -2     
+ Misses      26938    26936    -2     

Flag	Coverage Δ
rust	73.59% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/stream/src/from_proto/batch_query.rs	33.78% <0.00%> (+1.73%)	⬆️
src/meta/src/hummock/mock_hummock_meta_client.rs	42.39% <0.00%> (-1.09%)	⬇️
src/meta/src/barrier/mod.rs	69.13% <0.00%> (-0.33%)	⬇️
src/storage/src/hummock/local_version_manager.rs	84.12% <0.00%> (-0.16%)	⬇️
src/common/src/types/ordered_float.rs	24.90% <0.00%> (+0.19%)	⬆️

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