The above isnt required unless cross domain tracking from main site to another domain eg example.com cross tracking to someothersite.com

So simply install the default tracking code setup if you are not cross domain tracking.

Tracking itself is tied to the UA# within the tracking code.. eg i could take a copy of your tracking code .. place it on my site and my data would start to appear within your GA reports.

1) Do not include tracking code on the pages on dev.example.com

2) create and apply a filter to the profile that is tracking the main domain www.example com

Filter type - Custom

Include

Filter field - Hostname

Filter pattern - example\.com

Case sensitive.. no

Please keep in mind.. changes in tracking can take 24-48hrs to appear in reports.. 

Filters do not remove historical data, they only work going forward from the time they are created and applied to the profile