utils: use g_usleep() instead of my_usleep()

Now that I've found this nice function in the GLib docs, we can
finally remove our custom sleep function.  Still all those callers of
g_usleep() have to be migrated one day to use events, instead of
regular polling.

src/output/jack_plugin.c

@@ -16,7 +16,6 @@
  */
 
 #include "../output_api.h"
-#include "../utils.h"
 #include "config.h"
 
 #include <assert.h>
@@ -421,7 +420,7 @@ mpd_jack_play(void *data, const char *buff, size_t size)
 		} else {
 			/* XXX do something more intelligent to
 			   synchronize */
-			my_usleep(1000);
+			g_usleep(1000);
 		}
 
 	}

src/output/osx_plugin.c

@@ -17,7 +17,6 @@
  */
 
 #include "../output_api.h"
-#include "../utils.h"
 
 #include <glib.h>
 #include <AudioUnit/AudioUnit.h>
@@ -171,7 +170,7 @@ osx_render(void *vdata,
 	buffer->mDataByteSize = bufferSize;
 
 	if (!bufferSize) {
-		my_usleep(1000);
+		g_usleep(1000);
 	}
 
 	return 0;