Enforce DSP detection timeout.

Also remove separate detectFromDspSourceForTest() method. It originally
was serving different results for testing, but now it is practically
identical to the non-test method. Removing it allows us to exercise the
same code path in CTS tests as in production.

Bug: 212744476
Test: atest CtsVoiceInteractionTestCases
Test: Verify hotword detection works on Pixel 6 Pro
Change-Id: Ibb0c4f49fbfa64ed6c7362d355466a480c5979e2