Remove the old datasplitters from EvalML

[bchen1116]

Fix #2099

Note: I will likely merge this around the same time I merge 2128, which adds the sampler components to AutoMLSearch. This way, we will still maintain support for imbalanced datasets

[codecov]

Codecov Report

Merging #2193 (448d8fa) into main (fcacca2) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff            @@
##             main   #2193     +/-   ##
========================================
- Coverage   100.0%   99.9%   -0.0%     
========================================
  Files         288     280      -8     
  Lines       24610   24152    -458     
========================================
- Hits        24588   24127    -461     
- Misses         22      25      +3     

Impacted Files	Coverage Δ
evalml/preprocessing/data_splitters/__init__.py	100.0% <ø> (ø)
evalml/tests/automl_tests/test_automl.py	99.7% <ø> (ø)
evalml/preprocessing/__init__.py	100.0% <100.0%> (ø)
.../automl_tests/test_automl_search_classification.py	100.0% <100.0%> (ø)
evalml/tests/automl_tests/test_automl_utils.py	100.0% <100.0%> (ø)
evalml/automl/automl_search.py	99.0% <0.0%> (-0.5%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fcacca2...448d8fa. Read the comment docs.

[jeremyliweishih]

This looks good from my end. Must have been satisfying to delete all these files

[chukarsten]

RIP

[angela97lin]

✂️ ✂️ 👍

[dsherry]

Looks good to me!

[dsherry]

@bchen1116 oh I think you should also delete evalml/preprocessing/data_splitters/base_splitters.py.

[dsherry]

For those following along: the plan is to merge #2128 first, then this PR, and then that unblocks the oversampler work #2213