DEP: testing: disable deprecated use of keywords x/y

[mdhaber]

gh-24978 deprecated the use of keywords x and y in numpy.testing.assert_array_equal and numpy.testing.assert_array_almost_equal.

This PR removes the decorator that warned about the deprecation and allowed continued use of x and y; after the PR, only actual and desired are accepted.

[seberg]

Not that I think this is a big enough deprecation to worry, so happy if someone reviews+merges.

But on principle we should probably consider 2.0 and 2.1 a single release for deprecation purposes, in order to stay with the ~1 year of deprecation.

[mdhaber]

Oops, yeah. I forgot that 2.0 didn't come out until June. I'm happy to wait until 2.3; I had just set a reminder for one year because i didn't want to forget.

[charris]

Thanks @mdhaber .