Remove psutil hard dependency

[banesullivan]

This is a soft dependency and the only one that isn't readily available in the most minimal Python environments (pyodide).

Removing psutil should make the following source modules installable in pyodide (from a quick glance at dependencies... need to verify these actually work though)

• large-image-source-deepzoom
• large-image-source-dicom
• large-image-source-openjpeg
• large-image-source-pil
• large-image-source-vips

It is well handled if psutil is missing:

large_image/large_image/cache_util/cachefactory.py

Lines 96 to 99 in f7e664a

	if psutil:
	memory = psutil.virtual_memory().total
	else:
	memory = 1024 ** 3

and the only other place it is used is in large-image-converter (and the girder modules) which has it as a hard dependency:

large_image/utilities/converter/setup.py

Line 64 in f7e664a

'psutil',

https://github.com/girder/girder/blob/d994d93a00257a17eeeab7e0b6fa4a54f5658550/setup.py#L39

[manthey]

Maybe we should move it to the performance extras_require?

[banesullivan]

Happy to .. wasn't sure which of those extras was the best fit, so I left it out. Will add there now.