Propose removing old unmaintained skcuda code

[kushalkolar]

Should probably remove all the cuda stuff from motion correction because it just confuses people, example: #1048 . skcuda is no longer maintained, last release was over 5 years ago, so it's very unlikely to work with any relatively recently CUDA version and GPU, and would be difficult to interface with any other software. Given these limitations I don't even have a way to test if this even works. If users want GPU accelerated NoRMCorre we should just redirect them to FIOLA or jnormcorre which do a great job.

CaImAn/caiman/motion_correction.py

Lines 1629 to 1636 in bb55800

	if HAS_CUDA and use_cuda:
	from skcuda.fft import Plan
	from skcuda.fft import fft as cudafft
	from skcuda.fft import ifft as cudaifft
	try:
	cudactx # type: ignore
	except NameError:
	init_cuda_process()

[pgunn]

It's not entirely unmaintained; the author seems to occasionally still be accepting patches, but no release in nine years isn't great.

I think this proposal seems reasonable; the other option would be to port it to some other framework (which would at least not require people to go out-of-codebase) but I'm not keen to volunteer for such work; unless someone else shows up keen to do that soon, removing these codepaths is probably a good idea.