[Python][CI] Simplify numpy and pandas version requirement in the wheel build testing requirements

We currently have this in our `requirements-wheel-test.txt`:

https://github.com/apache/arrow/blob/0b33c652a69b41db5146484ecdeb28c2f33963e6/python/requirements-wheel-test.txt#L8-L26

I think we could simplify this a lot (we are already not testing the minimum supported version exactly), as long as we install a different version as the one we build with (which nowadays is the latest numpy version)
For example I think we can do away with all the platform-specific parts, and just specify a numpy version for a certain Python version.