Clean up legacy linalg implementation from the backend

[npolina4]

Cleaned up legacy linalg implementation from the backend for speed up build and improve code coverage.

Changes was tested with numda-dpex component.

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• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
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[github-actions]

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

[antonwolfy]

The change allows significantly improve code coverage. Thank you @npolina4
Btw, it would be great to describe the change with more details in the PR description, stating the motivation and secured avoided impact on dependent component.

[ZzEeKkAa]

I've tested dpex with opencl:cpu and opencl:gpu on iGPU 12th gen - no breaking changes where spotted