Remove oversampling nullable handling

[jeremyliweishih]

Fixes #4013.

[codecov]

Codecov Report

Merging #4064 (280897b) into main (f7e5d40) will decrease coverage by 0.0%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            main   #4064     +/-   ##
=======================================
- Coverage   99.7%   99.7%   -0.0%     
=======================================
  Files        349     349             
  Lines      37523   37509     -14     
=======================================
- Hits       37405   37391     -14     
  Misses       118     118             

Impacted Files	Coverage Δ
...es/components/transformers/samplers/oversampler.py	100.0% <ø> (ø)
evalml/tests/component_tests/test_oversampler.py	100.0% <ø> (ø)

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[tamargrey]

These tests are going to fail unless we raise the min sklearn version, I think https://github.com/alteryx/evalml/actions/runs/4376580073/jobs/7658890406#step:8:4233 since sklearn 1.2.1 is going to still have problems with nullable types