DEPR: Remove NumericIndex from tests/arithmetic/
Removes `NumericIndex` from `pandas/tests/arithemetic/`.

I've tried quite a lot to generalize the tests here to be for all the numeric numpy dtypes, but it seems almost impossible. The main issue is that numexpr operations behave differently for many dtypes lower than 64-bit than python ones, and its behaviour just seems unpredictably different than the normal python ops.

The tests in this directory concern both indexes and series and non-64-bit dtypes weren't tested before, even though it was possible for Series, and I assume the reason for that is the same difficulty, though I don't know for sure.

xref #42717.
thx @topper-123 