Remove STHAL 2.4

This version was only created as an intermediate version for
development and was never intended for release. STHAL 3 (AIDL) has
feature-parity with this one and is intended for release.

Bug: 181996624
Test: Manual verification of soundtrigger use-cases.
Test: atest FrameworksServicesTests:SoundTriggerMiddlewareImplTest FrameworksServicesTests:SoundHw2CompatTest
Change-Id: Ie7babd2aa37b1cb2830656808cce540a0e143a09