audio-echo: cleanup and upgrade dependencies.

We don't have any JARs, so that's gone.

appcompat is defined by the version catalog, so switch to that. The
catalog does define 1.6.1 right now, so this is also an upgrade.

audio-echo/app/build.gradle

@@ -22,6 +22,5 @@ android {
 }
 
 dependencies {
-    implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation 'androidx.appcompat:appcompat:1.5.1'
+    implementation libs.appcompat
 }