Re: [sensors] Don't allocate response objects to avoid triggering GC

If sensor has `reading` property, which is an object, with properties,
 then developer in event might assume it is immutable and/or 
instanced. This could lead to confusion like:

```javascript
var lastReading = null;
accelerometer.onchange = function(reading) {
    if (lastReading) {
        var deltaX = reading.x - lastReading.x;
    }
    lastReading = reading;
}
```
Someone would be confused why this wouldn't work on assumption that 
reading was immutable objects.

But if there is no object involved, such as `sensor.x`, then:
```javascript
var lastX = null;
accelerometer.onchange = function() {
    if (lastX !== null) {
        var deltaX = this.x - lastX;
    }
    lastX = this.x;
}
```

There is much less chance to get confused in this case.

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Received on Wednesday, 7 December 2016 12:37:37 UTC