chore(fragmenter): clean up some outdated/verbose comments

[xxchan]

What's changed and what's your intention?

as title. The code are self-explanatory now, so they are not needed

Checklist

• [ ] I have written necessary docs and comments
• [ ] I have added necessary unit tests and integration tests

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #2077 (39815ca) into main (88612d9) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2077   +/-   ##
=======================================
  Coverage   70.81%   70.81%           
=======================================
  Files         633      633           
  Lines       81416    81412    -4     
=======================================
- Hits        57655    57653    -2     
+ Misses      23761    23759    -2     

Flag	Coverage Δ
rust	70.81% <ø> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
src/meta/src/stream/fragmenter/mod.rs	83.95% <ø> (-0.19%)	⬇️
src/connector/src/filesystem/file_common.rs	80.44% <0.00%> (-0.45%)	⬇️
src/common/src/types/ordered_float.rs	23.70% <0.00%> (+0.19%)	⬆️
.../src/executor/managed_state/aggregation/extreme.rs	90.29% <0.00%> (+0.26%)	⬆️

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