REF/API/DEPR: _holds_integer checks in plotting

[jbrockmendel]

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Reproducible Example

NA

Issue Description

In the plotting code we have a few places where we check self.data.columns._holds_integer and one on index.inferred_type. AFAICT these are almost equivalent to just checking the dtype of the columns/index, but with some corner cases for object-dtype indexes. I don't think we should be special-casing these corner cases. We should deprecate that special-casing and move to dtype-based checks.

Expected Behavior

NA

Installed Versions

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[lazarust]

@jbrockmendel and @lithomas1 I can take this!

[lazarust]

take