core: restore MPT collapsing logic

[roman-khimov]

Fix #1867, revert part of bf20db0.

[codecov]

Codecov Report

Merging #1885 (9b15ab4) into master (99ca0b2) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1885      +/-   ##
==========================================
+ Coverage   82.84%   82.92%   +0.08%     
==========================================
  Files         287      287              
  Lines       22759    22762       +3     
==========================================
+ Hits        18854    18875      +21     
+ Misses       2712     2691      -21     
- Partials     1193     1196       +3     

Impacted Files	Coverage Δ
pkg/core/blockchain.go	79.91% <100.00%> (+0.06%)	⬆️
pkg/services/oracle/request.go	53.23% <0.00%> (+5.75%)	⬆️
pkg/services/oracle/oracle.go	90.90% <0.00%> (+11.36%)	⬆️

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