Resolves setuptools "Package would be ignored" warnings

[oleksandr-pavlyk]

Resolves setuptools "Package would be ignored" warnings (see CI build log for example).

Removed MANIFEST.in, set include_package_data=False, added folders and files to package_data keyword
of setup command.

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• Have you added a test, reproducer or referred to an issue with a reproducer?
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• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• If this PR is a work in progress, are you opening the PR as a draft?

[coveralls]

coverage: 85.68%. remained the same when pulling 67c7dbf on heed-setuptools-warnings into 526f410 on master.

[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/1441/index.html

[github-actions]

Array API standard conformance tests for dpctl=0.15.1dev0=py310ha25a700_34 ran successfully.
Passed: 935
Failed: 65
Skipped: 119