Remove unused MTU variable in GAttrib struct

The MTU variable in GAttrib struct was not being used for any operation
so it should be removed.
diff --git a/attrib/gattrib.c b/attrib/gattrib.c
index ef10b5b..c4cfd95 100644
--- a/attrib/gattrib.c
+++ b/attrib/gattrib.c
@@ -41,7 +41,6 @@
 struct _GAttrib {
 	GIOChannel *io;
 	gint refs;
-	gint mtu;
 	guint read_watch;
 	guint write_watch;
 	guint timeout_watch;
@@ -397,7 +396,6 @@
 		return NULL;
 
 	attrib->io = g_io_channel_ref(io);
-	attrib->mtu = 512;
 	attrib->queue = g_queue_new();
 
 	attrib->read_watch = g_io_add_watch(attrib->io,