Remove Intent.ACSD from KEYCODE_SEARCH action in-app

Apps can't close system dialogs anymore due to abuse. If we branch to
launching the assistant, VoiceInteractionSession has the power to close
system dialogs (besides I suspect this code-path is unused).

Bug: 191131805
Test: In-app, adb shell input keycode KEYCODE_SEARCH, verify no crash
Change-Id: I2ef20e0a0d9f05c26747e4dfca5bdb6ec7bd1c1f