android-emu: Fix -Wunused-function warning

Change-Id: I55f26e97dfe7ae322eaebf97a4f361ae28dfdd2d
diff --git a/android-emu/android/base/ring_buffer.c b/android-emu/android/base/ring_buffer.c
index aa562b8..fb6845f 100644
--- a/android-emu/android/base/ring_buffer.c
+++ b/android-emu/android/base/ring_buffer.c
@@ -407,14 +407,6 @@
 
 void ring_buffer_yield() { }
 
-static void ring_buffer_sleep() {
-#ifdef _WIN32
-    Sleep(2);
-#else
-    usleep(2000);
-#endif
-}
-
 bool ring_buffer_wait_write(
     const struct ring_buffer* r,
     const struct ring_buffer_view* v,