Plane: disable CLI by default

it really isn't needed any more, and saves 20k of flash on APM2

ArduPlane/config.h

@@ -456,9 +456,12 @@
  # define SCALING_SPEED          15.0
 #endif
 
-// use this to completely disable the CLI
+// use this to completely disable the CLI. We now default the CLI to
+// off as it really is no longer needed except for special developer
+// testing. This also allows us to keep supporting the APM2 for a bit
+// longer, as it saves us 20k of flash
 #ifndef CLI_ENABLED
- # define CLI_ENABLED ENABLED
+ # define CLI_ENABLED DISABLE
 #endif
 
 // use this to disable geo-fencing