dropping deepdiff dependency for eq check between MMIFs

[keighrim]

fixes #311

[codecov]

Codecov Report

❌ Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.98%. Comparing base (4c8a890) to head (7fa50e7).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
mmif/serialize/model.py	94.73%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #328      +/-   ##
===========================================
+ Coverage    87.95%   87.98%   +0.02%     
===========================================
  Files           13       13              
  Lines         1661     1673      +12     
===========================================
+ Hits          1461     1472      +11     
- Misses         200      201       +1     

Flag	Coverage Δ
unittests	87.98% <96.29%> (+0.02%)	⬆️

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