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.
Change-Id: Ic490bbd0501ec593d741cf612f8fd995b7bb9c4e