Data: shave off a couple of bytes.

Just a primitive changeset to drop a couple of bytes:
1. Remove unused varialbe `rnotwhite` in `src/data.js` — doesn't change the size but clarifies the code;
2. Change the RegExp used to convert camelCase to dash.

Tested in all modern desktop browsers + iOS 7 + Android 4. I think it will also work in iOS 6 and Android 2.3
Just in case, performance test: http://jsperf.com/camelcase-to-dash

```
   raw     gz Sizes                                                            
245620  72741 dist/jquery.js                                                   
 84039  29325 dist/jquery.min.js                                               

   raw     gz Compared to master @ ce308e25e57a0a040cd1ea05f00bf1cc23c1bd8a    
    -2     -2 dist/jquery.js                                                   
    -2     -1 dist/jquery.min.js         
```
Nice, looks like this was some copy-pasta from https://github.com/jquery/jquery/blob/master/src/data/Data.js, where it _is_ used.