Remove redundant num_features arg from Classification model

[kaushikb11]

What does this PR do?

Remove num_features arg from Classification model

Fixes # (issue)

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[carmocca]

Mind annotating the rest of types in that signature?

[codecov]

Codecov Report

Merging #88 (659b138) into master (13acf78) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #88   +/-   ##
=======================================
  Coverage   86.63%   86.63%           
=======================================
  Files          45       45           
  Lines        1369     1369           
=======================================
  Hits         1186     1186           
  Misses        183      183           

Flag	Coverage Δ
unittests	86.63% <ø> (ø)

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Impacted Files	Coverage Δ
flash/vision/classification/model.py	100.00% <ø> (ø)

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[kaushikb11]

Mind annotating the rest of types in that signature?

@carmocca Done, thanks!