Adafruit_DHT will eventually crash

The manipulation of `bitidx` in Adafruit_DHT will eventually cause a segfault.  If `readDHT` is called repeatedly, this line:

```
    bits[bitidx++] = counter;
```

...will eventually increment `bitidx` beyond the end of the `bits` array.

This code (and the `bits` array) appear to be unused except for debugging and can be safely removed.
