Stop populating accessibility nodes with events

This mostly rolls back ag/710190, which caused
AccessibilityEvents to contain their source nodes. These
nodes were not completely accurate, and populating them
increases the overhead of AccessibilityEvents, particularly
when large numbers of content changes happen. Having the
service reload the node if it needs the update content
should be sufficient. I have fixed several bugs since this
change went in to address issues with the accessibility
cache containing stale data. I think ensuring that the newly
loaded data is up-to-date will fix whatever issues carrying
the node along was intended to fix.

Bug: 33961523
Test: A11y CTS still passes. I also tried TalkBack on a
couple of switch controls, which is where I have previously
seen the most issues with up-to-date announcements.

Change-Id: Ie5a70bb0e89d49255c6a4c1c83d32b755c06902f