[HA Audio Output] Remove unnecessary API call

Root Cause: It will print warning logs when active device changed, but
it is unnecessary because it removes strategy that did not exist.

Solution: Check if strategy had been set before remove it.

Bug: 293251163
Bug: 295457342
Test: atest HearingAidAudioRoutingHelperTest
Change-Id: Ie8f3e7df4516ac819f7fec1ddbf50524c6bacc56