health: registerCallback() and getHealthInfo() does not notify all callbacks

registerCallback() and getHealthInfo() unintentionally broadcast
health info to all callbacks, which has a performance impact.

* registerCallback() still invokes the new callback immediately
* getHealthInfo() does not call any callbacks at all.

Test: VTS test call getHealthInfo does not invoke update()
Bug: 117167903
Change-Id: Ida99fdd73831e747fbf2d65089c7c0e7661fe7c4