fix(strategy-tests): document delete transitions were selecting identity in complicated way

[pauldelucia]

Issue being fixed or feature implemented

Document delete transitions were using identity callback function to get the identity for signing, which was overcomplicated for the current purposes. That method is the way to do it if we're trying to delete documents that already exist, but for now, we're just deleting documents that were also created in the current strategy. In the future, I guess it would be better to have it done the original way but for now, this is simpler.

What was done?

Just get the identity from the current_identities

This means you can only delete documents that were created in the current strategy, but it's good enough for a first implementation. No other aspects of strategy tests in TUI really are compatible with previous strategy tests anyways.

How Has This Been Tested?

TUI

Breaking Changes

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