Revert "make jsonschema4 compatible (DeprecationWarning fix)"

[p1c2u]

This reverts commit c8813cb, reversing
changes made to b36c12b.

Removing the change from 0.2.x branch i will go to 0.3.x that will support jsonschema 4+

Fixes #31

[codecov]

Codecov Report

Merging #34 (6abc164) into stable/0.2.x (22c5892) will decrease coverage by 0.20%.
The diff coverage is 100.00%.

@@               Coverage Diff                @@
##           stable/0.2.x      #34      +/-   ##
================================================
- Coverage         62.29%   62.08%   -0.21%     
================================================
  Files                 6        6              
  Lines               183      182       -1     
  Branches             39       39              
================================================
- Hits                114      113       -1     
  Misses               54       54              
  Partials             15       15              

Impacted Files	Coverage Δ
openapi_schema_validator/validators.py	94.11% <100.00%> (-0.33%)	⬇️

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