Remove unnecessary Const

[pxl-th]

Fixes #2.

@Const on half_size_group is not needed, since it is an integer.
@Const on comparator function does not play well with AMDGPU for some reason (and I'm not sure it is needed), especially if it is a closure.

With these changes all tests on RX 7900XTX pass.
We probably should set up CI for testing.

[anicusan]

Thank you for investigating and the fix! It does not affect performance on my machines (still 1.10.5), so I will merge this now, at least as a temporary fix.

It is odd though that this error only seems to appear in Julia 1.11; I tested the AMDGPU backend two weeks ago on 1.10.5 and it worked fine. @vchuravy is this something you know of?

And a few questions:

1. Does @Const not make sense on integers or other POD types? In CUDA kernels they are used and can make a difference.
2. Should we remove @Const from other closures? They're used in a few other places too.

[vchuravy]

@Const only makes sense on array types, but it does use adapt so it might recursively go through structs