chore(storage): remove redundant Result on serialize_pk

[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 #3088 (940082d) into main (77e07f0) will decrease coverage by 0.00%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main    #3088      +/-   ##
==========================================
- Coverage   73.40%   73.40%   -0.01%     
==========================================
  Files         734      734              
  Lines       99959    99961       +2     
==========================================
- Hits        73376    73374       -2     
- Misses      26583    26587       +4     

Flag	Coverage Δ
rust	73.40% <50.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/storage/src/table/cell_based_table.rs	72.61% <18.18%> (-0.36%)	⬇️
src/storage/src/table/state_table.rs	86.79% <66.66%> (-1.19%)	⬇️
src/common/src/util/ordered/serde.rs	91.06% <100.00%> (ø)
src/storage/src/table/test_relational_table.rs	98.21% <100.00%> (ø)

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