Remove deprecated get_memory_profile

[puhuk]

To resolve issue #12521

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[akihironitta]

@puhuk Would you mind removing the deprecated function from the following test case?
https://github.com/PyTorchLightning/pytorch-lightning/blob/c233731b7c55d2533ab76eecf609e8df0e0ebfc3/tests/deprecated_api/test_remove_1-7.py#L54