Revert "core: remove Echidna compatibility code from registerCandidate"

[AnnaShaleva]

This reverts commit a0c3d77 since it affects execution results. Close #4262.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.49%. Comparing base (a827b71) to head (4d6cc69).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/core/native/native_neo.go	33.33%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4273      +/-   ##
==========================================
- Coverage   83.49%   83.49%   -0.01%     
==========================================
  Files         359      359              
  Lines       44158    44164       +6     
==========================================
+ Hits        36871    36875       +4     
+ Misses       5471     5470       -1     
- Partials     1816     1819       +3     

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