Remove the Image<->np.ndarray equality comparison support

[IRDonch]

Summary

This support has some questionable semantics:

• It's not symmetric (Image can be equal to ndarray, but not the other way around).

• It doesn't behave the same as ndarray comparison (which returns an ndarray rather than bool), so it's not quite transitive either (if image == array1 and image == array2 are true, then array1 == array2 is not true (but an array of Trues).

Moreover, it's seemingly only used in two tests, and those tests can easily use np.testing.assert_array_equal instead, which has the added benefit of printing detailed mismatch information.

Inspired by the discussion in #521.

How to test

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[zhiltsov-max]

I'm not sure I'm totally agree with removing underused functionality, but the semantics point looks more or less significant. But I see it more like a Python design problem.