Revert "Create a system API to allow preinstalled assistants to receive training data events."

This reverts commit d4051e73.

Revert Reason: Deprecate trusted fed-hot.
Test: atest -c CtsVoiceInteractionTestCases:HotwordDetectionServiceBasicTest
Bug:322391277


Change-Id: I9a73cc03c19eaca489dd7ad3d665b752191c289e