Remove Int64Index after Pandas 1.5 Upgrade

[christopherbunn]

Blocked on #3759
Resolves #3760

[codecov]

Codecov Report

Merging #3825 (4066e31) into main (53a4912) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main   #3825     +/-   ##
=======================================
- Coverage   99.7%   99.7%   -0.0%     
=======================================
  Files        344     344             
  Lines      36211   36209      -2     
=======================================
- Hits       36074   36072      -2     
  Misses       137     137             

Impacted Files	Coverage Δ
...omponents/transformers/preprocessing/decomposer.py	99.3% <100.0%> (-<0.1%)	⬇️
...ransformers/preprocessing/polynomial_decomposer.py	100.0% <100.0%> (ø)
...nents/transformers/preprocessing/stl_decomposer.py	100.0% <100.0%> (ø)

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[jeremyliweishih]

LGTM - we should be good with existing coverage