refactor: Remove bluebird from test/unit/lib/classes

[juanjoDiaz]

Addresses: #7171

[codecov]

Codecov Report

Merging #9070 (a3c22fb) into master (ccba70a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #9070   +/-   ##
=======================================
  Coverage   87.15%   87.15%           
=======================================
  Files         288      288           
  Lines       11026    11026           
=======================================
  Hits         9610     9610           
  Misses       1416     1416           

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[pgrzesik]

Thanks once again @juanjoDiaz - as mentioned in related PR, we'd like to follow more iterative, small-steps path - I'm going to close this PR for now.