chore: remove unused codes for samples

[zhaoyongjie]

SUMMARY

the PR introduced a new endpoint for getting samples from datasets, so remove unused codes.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

No functions change.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #20272 (e3f58dc) into master (77e326f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #20272   +/-   ##
=======================================
  Coverage   66.65%   66.65%           
=======================================
  Files        1729     1729           
  Lines       64904    64900    -4     
  Branches     6842     6842           
=======================================
- Hits        43262    43260    -2     
+ Misses      19893    19891    -2     
  Partials     1749     1749           

Flag	Coverage Δ
javascript	51.57% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
...uperset-frontend/src/explore/exploreUtils/index.js	80.59% <100.00%> (+0.88%)	⬆️

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[stephenLYZ]

LGTM