rpc: adjust getutxotransfers RPC

[fyrchik]

Close #1287 .
The only thing that bothers me is that total_amount field is somewhat meaningless now.

[codecov]

Codecov Report

Merging #1288 into master-2.x will decrease coverage by 0.07%.
The diff coverage is 62.50%.

@@              Coverage Diff               @@
##           master-2.x    #1288      +/-   ##
==============================================
- Coverage       67.75%   67.68%   -0.08%     
==============================================
  Files             160      160              
  Lines           15892    15851      -41     
==============================================
- Hits            10768    10729      -39     
- Misses           4584     4588       +4     
+ Partials          540      534       -6     

Impacted Files	Coverage Δ
pkg/core/state/transfer_log.go	50.00% <50.00%> (ø)
pkg/core/blockchain.go	44.55% <56.00%> (-1.00%)	⬇️
pkg/rpc/server/server.go	83.92% <100.00%> (-0.14%)	⬇️
pkg/core/mpt/trie.go	92.43% <0.00%> (-0.43%)	⬇️

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