DEPR: Remove NumericIndex
- [x] closes #42717
- [x] closes #51020

This finishes the removal of `NumericIndex` from the code base. Note that this PR builds atop of #51132, so you might want to merge that first.

Everything should be finished now after this PR, e.g. the doc updates  have been merged (#51111) and the doc string has been updated (#51089). I'll have a final look once this is merged, but this should pretty much finish this issue. 
thx @topper-123  This removal is the partially the cause of a regression unpickling files from "pandas<2", #53300 This remove action caused a bug `ModuleNotFoundError: No module named 'pandas.core.indexes.numeric` when use `pandas>=2.0.0 `