chore: remove obsolete fetchExploreJson function

[john-bodley]

SUMMARY

Whilst spelunking in the code I realized that the fetchExploreJson method wasn't used outside of testing and thus warranted being deleted.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

CI.

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 #24669 (0a739ce) into master (1473d97) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 0a739ce differs from pull request most recent head 1610cec. Consider uploading reports for the commit 1610cec to get more accurate results

@@            Coverage Diff             @@
##           master   #24669      +/-   ##
==========================================
- Coverage   69.03%   69.02%   -0.01%     
==========================================
  Files        1908     1907       -1     
  Lines       74197    74190       -7     
  Branches     8186     8181       -5     
==========================================
- Hits        51219    51212       -7     
  Misses      20857    20857              
  Partials     2121     2121              

Flag	Coverage Δ
javascript	55.71% <ø> (-0.01%)	⬇️

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