Fix suggestions logic (2014.1 branch)

**This is #11648, cherrypicked for 2014.1**

This code was previously repeating the same action (setting the
suggestions key for the given package to list(provides) once for every
element in the set. While this did not produce a functionally incorrect
result, it is unnecessary and poorly-constructed as-is. This commit
simplifies the logic, and only performs that action once.