Remove obsolete dparray interface

[antonwolfy]

dpnp.dparray interface is obsolete and has not been updated for a long time. It's not assumed to be used.
Instead here is dpnp.ndarray interface which is aligning with numpy.ndarray one.

The PR proposes to clean the code and to remove the obsolete interface.

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[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html