Fix S4487: Unread "private" fields should be removed

[bart-vmware]

Description

This PR removes private fields that are unused or only assigned but never read.

If during review, you find any cases where the field should not be removed, please indicate how to update existing code to read from the field and use its value.

Fixes #954.

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[bart-vmware]

As @hananiel pointed out elsewhere, it may be necessary to keep fields of reference types that aren't read from, just to extend their lifetime and prevent them from being garbage-collected. That's a legitimate case to suppress warnings.