Remove LevelDb from dependencies

[Harrm]

Referenced issues

Description of the Change

LevelDb dependencies are removed from kagome code, but LevelDb is still in Hunter dependencies.

Benefits

Faster build.

Possible Drawbacks

None expected.

[codecov]

Codecov Report

Merging #1380 (d259d91) into master (db19edf) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

❗ Current head d259d91 differs from pull request most recent head 04d8b5c. Consider uploading reports for the commit 04d8b5c to get more accurate results

@@            Coverage Diff             @@
##           master    #1380      +/-   ##
==========================================
- Coverage   24.58%   24.58%   -0.01%     
==========================================
  Files         629      629              
  Lines       23613    23613              
  Branches    12288    12288              
==========================================
- Hits         5806     5805       -1     
  Misses      12540    12540              
- Partials     5267     5268       +1     

Impacted Files	Coverage Δ
core/storage/in_memory/in_memory_storage.hpp	100.00% <ø> (ø)
core/storage/rocksdb/rocksdb_util.hpp	52.38% <0.00%> (ø)
core/api/transport/impl/ws/ws_listener_impl.cpp	41.66% <0.00%> (-1.39%)	⬇️

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