Revert "Introduce ActivityTransactionItem and reduce null checks"

This reverts commit 9b1e955021ce4ce8c09b26c5fb38a2bb9c5a2d6d.

Reason for revert: Breaks many tests

Bug: 164982975
Change-Id: I86e7b158ae593aab6d73950bbb2b9dc6a7d5093c
23 files changed