Restores and fixes `cancel-us-users` drush task

#### What's this PR do?
- Restores `cancel-us-users` from 6954a14
- Adds a condition to skip users with any node content create: 1fdc063

#### Testing
Node count in `2014-11-20-185511.uk.sql.gz`:
 ![screen shot 2014-11-25 at 8 56 12 pm](https://cloud.githubusercontent.com/assets/672669/5189991/c65f52d8-74ea-11e4-8614-3644119cf888.png)

After running the original script on only **10** users it removed `886` nodes out of `1138`:
![screen shot 2014-11-25 at 9 10 06 pm copy](https://cloud.githubusercontent.com/assets/672669/5190002/dac230ce-74ea-11e4-8553-6f5d063a6cce.png)

After running the modified script run **1000** users it's still `1138` nodes:
![screen shot 2014-11-25 at 9 29 48 pm](https://cloud.githubusercontent.com/assets/672669/5190029/014b0dc4-74eb-11e4-9375-600e632ba698.png)
12 users were not deleted compared to the original script.

#### What are the relevant tickets?
A part of #3552