libeffects: Add host support for preprocessing module

- Removed __unused that is not supported by host toolchain

Bug: 182485928
Test: AudioPreProcessingTest on host

Change-Id: I5b87ab71a7c785e5dc610770ddfe141864874c2b
diff --git a/media/libeffects/preprocessing/Android.bp b/media/libeffects/preprocessing/Android.bp
index eb3ce34..37b2ae0 100644
--- a/media/libeffects/preprocessing/Android.bp
+++ b/media/libeffects/preprocessing/Android.bp
@@ -22,6 +22,7 @@
     name: "libaudiopreprocessing",
     vendor: true,
     relative_install_path: "soundfx",
+    host_supported: true,
     srcs: ["PreProcessing.cpp"],
     local_include_dirs: [
         ".",