Remove Pivot Reporting infrastructure

[benbowler]

Feature Description

The ability to make Pivot Report requests to the GA Data API was added in #8811 for the Audience Segmentation feature. However this was not fit for purpose and was not used while being left in the code base.

This additional code adds un-needed complexity and should be removed.

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Acceptance criteria

Implementation Brief

Note for the IB writer, the majority of this work is in this PR which can be used as a base as to what needs to be reverted.

Test Coverage

QA Brief

Changelog entry