DataUsageUtils: Clean up based on code review

* Add missing header
* Extract DataUsageContract.UID + " = ? " into a string
* Simplify "0" string
* Use try-with-resource block to ensure cursor is closed

This commit is based on the post-merge feedback of Kamaljeet Maini,
Fabrice Di Meglio and Danny Baumann.

RM-290

Change-Id: I774948ba119e3e4a2dd438e1ed1588bfb9fefae2