Remove very repeated calls to onMergedOverrideConfigurationChanged

Somehow we got to the point where we are calling this repeatedly
for a single config change: onCfgChg calls onMerged which
internally calls onMerged for whole subtree. But then, onCfgChg
also walks the whole subtree, so we end up calling onMerged
many times.

Bug: 202201326
Test: this is functionally no-op, so existing tests.
Change-Id: I6a5b5936c8afc51022532880647f7342f5fd22d1